Shoshana Williams

All Publications

• Structure and mechanism of the alkane-oxidizing enzyme AlkB. Nature communications Guo, X., Zhang, J., Han, L., Lee, J., Williams, S. C., Forsberg, A., Xu, Y., Austin, R. N., Feng, L. 2023; 14 (1): 2180

  Abstract

  Alkanes are the most energy-rich form of carbon and are widely dispersed in the environment. Their transformation by microbes represents a key step in the global carbon cycle. Alkane monooxygenase (AlkB), a membrane-spanning metalloenzyme, converts straight chain alkanes to alcohols in the first step of the microbially-mediated degradation of alkanes, thereby playing a critical role in the global cycling of carbon and the bioremediation of oil. AlkB biodiversity is attributed to its ability to oxidize alkanes of various chain lengths, while individual AlkBs target a relatively narrow range. Mechanisms of substrate selectivity and catalytic activity remain elusive. Here we report the cryo-EM structure of AlkB, which provides a distinct architecture for membrane enzymes. Our structure and functional studies reveal an unexpected diiron center configuration and identify molecular determinants for substrate selectivity. These findings provide insight into the catalytic mechanism of AlkB and shed light on its function in alkane-degrading microorganisms.

  View details for DOI 10.1038/s41467-023-37869-z

  View details for PubMedID 37069165

  View details for PubMedCentralID 4640736

• An alkane monooxygenase (AlkB) family in which all electron transfer partners are covalently bound to the oxygen-activating hydroxylase JOURNAL OF INORGANIC BIOCHEMISTRY Williams, S. C., Luongo, D., Orman, M., Vizcarra, C. L., Austin, R. N. 2022; 228: 111707

  Abstract

  Alkane monooxygenase (AlkB) is a non-heme diiron enzyme that catalyzes the hydroxylation of alkanes. It is commonly found in alkanotrophic organisms that can live on alkanes as their sole source of carbon and energy. Activation of AlkB occurs via two-electron reduction of its diferric active site, which facilitates the binding, activation, and cleavage of molecular oxygen for insertion into an inert CH bond. Electrons are typically supplied by NADH via a rubredoxin reductase (AlkT) to a rubredoxin (AlkG) to AlkB, although alternative electron transfer partners have been observed. Here we report a family of AlkBs in which both electron transfer partners (a ferredoxin and a ferredoxin reductase) appear as an N-terminal gene fusion to the hydroxylase (ferr_ferrR_AlkB). This enzyme catalyzes the hydroxylation of medium chain alkanes (C6-C14), with a preference for C10-C12. It requires only NADH for activity. It is present in a number of bacteria that are known to be human pathogens. A survey of the genome neighborhoods in which is it found suggest it may be involved in alkane metabolism, perhaps facilitating growth of pathogens in non-host environments.

  View details for DOI 10.1016/j.jinorgbio.2021.111707

  View details for Web of Science ID 000789398900004

  View details for PubMedID 34990970

  View details for PubMedCentralID PMC8799515

• An Overview of the Electron-Transfer Proteins That Activate Alkane Monooxygenase (AlkB). Frontiers in microbiology Williams, S. C., Austin, R. N. 2022; 13: 845551

  Abstract

  Alkane-oxidizing enzymes play an important role in the global carbon cycle. Alkane monooxygenase (AlkB) oxidizes most of the medium-chain length alkanes in the environment. The first AlkB identified was from P. putida GPo1 (initially known as P. oleovorans) in the early 1970s, and it continues to be the family member about which the most is known. This AlkB is found as part of the OCT operon, in which all of the key proteins required for growth on alkanes are present. The AlkB catalytic cycle requires that the diiron active site be reduced. In P. putida GPo1, electrons originate from NADH and arrive at AlkB via the intermediacy of a flavin reductase and an iron-sulfur protein (a rubredoxin). In this Mini Review, we will review what is known about the canonical arrangement of electron-transfer proteins that activate AlkB and, more importantly, point to several other arrangements that are possible. These other arrangements include the presence of a simpler rubredoxin than what is found in the canonical arrangement, as well as two other classes of AlkBs with fused electron-transfer partners. In one class, a rubredoxin is fused to the hydroxylase and in another less well-explored class, a ferredoxin reductase and a ferredoxin are fused to the hydroxylase. We review what is known about the biochemistry of these electron-transfer proteins, speculate on the biological significance of this diversity, and point to key questions for future research.

  View details for DOI 10.3389/fmicb.2022.845551

  View details for PubMedID 35295299