I am curious about how life emerges from fundamental chemical and biochemical building blocks. I use a wide range of tools from membrane physics, organic chemistry, and biochemistry to address these questions. I am passionate about communicating science and making it a transformational force for betterment of society and humanity.
Honors & Awards
Prime Minister of India Gold Medal, Indian Institute of Technology Kharagpur (2014)
Teddy Traylor Award 2018, University of California San Diego (2018)
Reaxys PhD Prize 2020 Finalist, Elsevier (2020)
Bachelor of Science, Indian Institute of Technology, Kharagpur (2014)
Master of Science, Indian Institute of Technology, Kharagpur (2014)
Doctor of Philosophy, University of California San Diego (2020)
MSc, Indian Institute of Technology Kharagpur, Chemistry (2014)
PhD, University of California San Diego, Chemistry (2020)
Steven Boxer, Postdoctoral Faculty Sponsor
Expression of Fatty Acyl-CoA Ligase Drives One-Pot De Novo Synthesis of Membrane-Bound Vesicles in a Cell-Free Transcription-Translation System
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2021; 143 (29): 11235-11242
Despite the central importance of lipid membranes in cellular organization, it is challenging to reconstitute their formation de novo from minimal chemical and biological elements. Here, we describe a chemoenzymatic route to membrane-forming noncanonical phospholipids in which cysteine-modified lysolipids undergo spontaneous coupling with fatty acyl-CoA thioesters generated enzymatically by a fatty acyl-CoA ligase. Due to the high efficiency of the reaction, we were able to optimize phospholipid formation in a cell-free transcription-translation (TX-TL) system. Combining DNA encoding the fatty acyl-CoA ligase with suitable lipid precursors enabled one-pot de novo synthesis of membrane-bound vesicles. Noncanonical sphingolipid synthesis was also possible by using a cysteine-modified lysosphingomyelin as a precursor. When the sphingomyelin-interacting protein lysenin was coexpressed alongside the acyl-CoA ligase, the in situ assembled membranes were spontaneously decorated with protein. Our strategy of coupling gene expression with membrane lipid synthesis in a one-pot fashion could facilitate the generation of proteoliposomes and brings us closer to the bottom-up generation of synthetic cells using recombinant synthetic biology platforms.
View details for DOI 10.1021/jacs.1c05394
View details for Web of Science ID 000679913600051
View details for PubMedID 34260248
Enantioselective Total Synthesis of the Archaeal Lipid Parallel GDGT-0 (Isocaldarchaeol).
Angewandte Chemie (International ed. in English)
Archaeal glycerol dibiphytanyl glycerol tetraethers (GDGT) are some of the most unusual membrane lipids identified in nature. These amphiphiles are the major constituents of the membranes of numerous Archaea, some of which are extremophilic organisms. Due to their unique structures, there has been significant interest in studying both the biophysical properties and the biosynthesis of these molecules. However, these studies have thus far been hampered by limited access to chemically pure samples. Herein, we report a concise and stereoselective synthesis of the archaeal tetraether lipid parallel GDGT-0 and the synthesis and self-assembly of derivatives bearing different polar groups.
View details for DOI 10.1002/anie.202104051
View details for PubMedID 33930240
Enzyme-free synthesis of natural phospholipids in water
2020; 12 (11): 1029-+
All living organisms synthesize phospholipids as the primary constituent of their cell membranes. Enzymatic synthesis of diacylphospholipids requires preexisting membrane-embedded enzymes. This limitation has led to models of early life in which the first cells used simpler types of membrane building blocks and has hampered integration of phospholipid synthesis into artificial cells. Here we demonstrate an enzyme-free synthesis of natural diacylphospholipids by transacylation in water, which is enabled by a combination of ion pairing and self-assembly between lysophospholipids and acyl donors. A variety of membrane-forming cellular phospholipids have been obtained in high yields. Membrane formation takes place in water from natural alkaline sources such as soda lakes and hydrothermal oceanic vents. When formed vesicles are transferred to more acidic solutions, electrochemical proton gradients are spontaneously established and maintained. This high-yielding non-enzymatic synthesis of natural phospholipids in water opens up new routes for lipid synthesis in artificial cells and sheds light on the origin and evolution of cellular membranes.
View details for DOI 10.1038/s41557-020-00559-0
View details for Web of Science ID 000577065000001
View details for PubMedID 33046841
Lipid sponge droplets as programmable synthetic organelles
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2020; 117 (31): 18206–15
Living cells segregate molecules and reactions in various subcellular compartments known as organelles. Spatial organization is likely essential for expanding the biochemical functions of synthetic reaction systems, including artificial cells. Many studies have attempted to mimic organelle functions using lamellar membrane-bound vesicles. However, vesicles typically suffer from highly limited transport across the membranes and an inability to mimic the dense membrane networks typically found in organelles such as the endoplasmic reticulum. Here, we describe programmable synthetic organelles based on highly stable nonlamellar sponge phase droplets that spontaneously assemble from a single-chain galactolipid and nonionic detergents. Due to their nanoporous structure, lipid sponge droplets readily exchange materials with the surrounding environment. In addition, the sponge phase contains a dense network of lipid bilayers and nanometric aqueous channels, which allows different classes of molecules to partition based on their size, polarity, and specific binding motifs. The sequestration of biologically relevant macromolecules can be programmed by the addition of suitably functionalized amphiphiles to the droplets. We demonstrate that droplets can harbor functional soluble and transmembrane proteins, allowing for the colocalization and concentration of enzymes and substrates to enhance reaction rates. Droplets protect bound proteins from proteases, and these interactions can be engineered to be reversible and optically controlled. Our results show that lipid sponge droplets permit the facile integration of membrane-rich environments and self-assembling spatial organization with biochemical reaction systems.
View details for DOI 10.1073/pnas.2004408117
View details for Web of Science ID 000573679600017
View details for PubMedID 32694212
View details for PubMedCentralID PMC7414067
Temperature-Dependent Reversible Morphological Transformations in N-Oleoyl beta-D-Galactopyranosylamine
JOURNAL OF PHYSICAL CHEMISTRY B
2020; 124 (26): 5426–33
Amphiphilic molecules self-assemble into supramolecular structures of various sizes and morphologies depending on their molecular packing and external factors. Transformations between various self-assembled morphologies are a matter of great fundamental interest. Recently, we reported the discovery of a novel class of single-chain galactopyranosylamide amphiphiles that self-assemble to form vesicles in water. Here, we describe how the vesicles composed of the amphiphile N-oleoyl β-d-galactopyranosylamine (GOA) undergo a morphological transition to fibers consisting of mainly flat sheet-like structures. Moreover, we show that this transformation is reversible in a temperature-dependent manner. We used several optical microscopy and electron microscopy techniques, circular dichroism spectroscopy, small-angle X-ray scattering, and differential scanning calorimetry, to fully investigate and characterize the morphological transformations of GOA and provide a structural basis for such phenomena. These studies provide significant molecular insight into the structural polymorphism of sugar-based amphiphiles and foresee future applications in rational design of self-assembled materials.
View details for DOI 10.1021/acs.jpcb.0c01410
View details for Web of Science ID 000547453400010
View details for PubMedID 32437154
Tailoring the Shape and Size of Artificial Cells
2019; 13 (7): 7396–7401
Living cells achieve precise control of shape and size through sophisticated biochemical machinery. However, such precision is extremely challenging to emulate in artificial cellular compartments. So far, various physicochemical and mechanical interventions have been employed to tailor the dimensions of model systems such as liposomes, emulsions, coacervates, and polymer capsules. In this Perspective, we discuss the state of the art in artificial cell research in controlling shape and size and the challenges that need to be addressed.
View details for DOI 10.1021/acsnano.9b05112
View details for Web of Science ID 000477786400006
View details for PubMedID 31298028
Single-Chain beta-D-Glycopyranosylamides of Unsaturated Fatty Acids: Self-Assembly Properties and Applications to Artificial Cell Development
JOURNAL OF PHYSICAL CHEMISTRY B
2019; 123 (17): 3711–20
Amphiphilic molecules undergo self-assembly in aqueous medium to yield various supramolecular structures depending on their chemical structure and molecular geometry. Among these, lamellar membrane-bound vesicles are of special interest due to their resemblance to cellular membranes. Here we describe the self-assembly of single-chain amide-linked amphiphiles derived from β-d-galactopyranosylamine and various unsaturated fatty acids into vesicles. In contrast, the analogous amphiphiles derived from β-d-glucopyranosylamine self-assemble into nanotubes. Fluorescence spectroscopy, X-ray diffraction, and differential scanning calorimetry are used to determine various physical parameters pertinent to the self-assembly process. The vesicular architecture is characterized using optical microscopy and transmission electron microscopy. Moreover, we show that the vesicles derived from these amphiphiles can encapsulate molecules of various sizes and host model biochemical reactions. Our work demonstrates that single-chain glycolipid-based amphiphiles could serve as robust building blocks for artificial cells and have potential applications in drug delivery and microreactor design.
View details for DOI 10.1021/acs.jpcb.9b01055
View details for Web of Science ID 000466989000018
View details for PubMedID 30964979
A minimal biochemical route towards de novo formation of synthetic phospholipid membranes
2019; 10: 300
All living cells consist of membrane compartments, which are mainly composed of phospholipids. Phospholipid synthesis is catalyzed by membrane-bound enzymes, which themselves require pre-existing membranes for function. Thus, the principle of membrane continuity creates a paradox when considering how the first biochemical membrane-synthesis machinery arose and has hampered efforts to develop simplified pathways for membrane generation in synthetic cells. Here, we develop a high-yielding strategy for de novo formation and growth of phospholipid membranes by repurposing a soluble enzyme FadD10 to form fatty acyl adenylates that react with amine-functionalized lysolipids to form phospholipids. Continuous supply of fresh precursors needed for lipid synthesis enables the growth of vesicles encapsulating FadD10. Using a minimal transcription/translation system, phospholipid vesicles are generated de novo in the presence of DNA encoding FadD10. Our findings suggest that alternate chemistries can produce and maintain synthetic phospholipid membranes and provides a strategy for generating membrane-based materials.
View details for DOI 10.1038/s41467-018-08174-x
View details for Web of Science ID 000455954700001
View details for PubMedID 30655537
View details for PubMedCentralID PMC6336818
Highly Stable Artificial Cells from Galactopyranose-Derived Single-Chain Amphiphiles
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2018; 140 (50): 17356–60
Single-chain amphiphiles (SCAs) that self-assemble into large vesicular structures are attractive components of synthetic cells because of the simplicity of bilayer formation and increased membrane permeability. However, SCAs commonly used for vesicle formation suffer from restricted working pH ranges, instability to divalent cations, and the inhibition of biocatalysts. Construction of more robust biocompatible membranes from SCAs would have significant benefits. We describe the formation of highly stable vesicles from alkyl galactopyranose thioesters. The compatibility of these uncharged SCAs with biomolecules makes possible the encapsulation of functional enzymes and nucleic acids during the vesicle generation process, enabling membrane protein reconstitution and compartmentalized nucleic acid amplification, even when charged precursors are supplied externally.
View details for DOI 10.1021/jacs.8b09388
View details for Web of Science ID 000454383400006
View details for PubMedID 30495932
In Situ Lipid Membrane Formation Triggered by Intramolecular Photoinduced Electron Transfer
2018; 34 (3): 750–55
A major goal of synthetic biology is the development of rational methodologies to construct self-assembling non-natural membranes, which could enable the efficient fabrication of artificial cellular systems from purely synthetic components. However, spatiotemporal control of artificial membrane formation remains both challenging and limited in scope. Here, we describe a new methodology to promote biomimetic phospholipid membrane formation by the photochemical activation of a catalyst-sensitizer dyad via an intramolecular photoinduced electron-transfer process. Our results offer future opportunities to exert spatiotemporal control over artificial cellular constructs.
View details for DOI 10.1021/acs.langmuir.7b02783
View details for Web of Science ID 000423418300004
View details for PubMedID 28982007
De novo vesicle formation and growth: an integrative approach to artificial cells
2017; 8 (12): 7912–22
The assembly of artificial cells provides a novel strategy to reconstruct life's functions and shed light on how life emerged on Earth and possibly elsewhere. A major challenge to the development of artificial cells is the establishment of simple methodologies to mimic native membrane generation. An ambitious strategy is the bottom-up approach, which aims to systematically control the assembly of highly ordered membrane architectures with defined functionality. This perspective will cover recent advances and the current state-of-the-art of minimal lipid architectures that can faithfully reconstruct the structure and function of living cells. Specifically, we will overview work related to the de novo formation and growth of biomimetic membranes. These studies give us a deeper understanding of the nature of living systems and bring new insights into the origin of cellular life.
View details for DOI 10.1039/c7sc02339a
View details for Web of Science ID 000415877000003
View details for PubMedID 29619165
View details for PubMedCentralID PMC5858084
Synthesis of functionalised azepanes and piperidines from bicyclic halogenated aminocyclopropane derivatives
ORGANIC & BIOMOLECULAR CHEMISTRY
2017; 15 (25): 5364–72
A series of 6,6-dihalo-2-azabicyclo[3.1.0]hexane and 7,7-dihalo-2-azabicyclo[4.1.0]heptane compounds were prepared by the reaction of dihalocarbene species with N-Boc-2,3-dihydro-1H-pyrroles or -1,2,3,4-tetrahydropyridines. Monochloro substrates were synthesised as well, using a chlorine-to-lithium exchange reaction. The behaviour of several aldehydes and ketones under reductive amination conditions with deprotected halogenated secondary cyclopropylamines was investigated, showing that this transformation typically triggers cyclopropane ring cleavage to give access to interesting nitrogen-containing ring-expanded products.
View details for DOI 10.1039/c7ob01238a
View details for Web of Science ID 000404358300019
View details for PubMedID 28617508
- Spontaneous Phospholipid Membrane Formation by Histidine Ligation SYNLETT 2017; 28 (1): 108–12
- Polyaromatic label-assisted laser desorption ionization mass spectrometry (LA-LDI MS): a new analytical technique for selective detection of zinc ion RSC ADVANCES 2014; 4 (44): 23314–18