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8.A.46 The Glycan-binding Protein (SusD) Family

Bacteroides thetaiotaomicron, a gram-negative obligate anaerobe, utilizes polysaccharides by binding them to its cell surface and allowing cell-associated enzymes to hydrolyze them into digestible fragments. Reeves et al. 1997 used the starch utilization system as a model to analyze the initial steps involved in polysaccharide binding and breakdown. 14C-Starch binding assays showed that SusC and SusD both contribute to starch binding, that  SusC and SusD interact in the outer membrane, and that they  are exposed to the cell surface.

Koropatkin et al. 2009 presented the atomic structure of the B. thetaiotaomicron protein BT1043, an outer membrane lipoprotein involved in host glycan metabolism that is a structural homologue of the B. thetaiotaomicron starch-binding protein SusD. Both structures are dominated by tetratrico peptide repeats that may facilitate association with outer membrane beta-barrel transporters required for glycan uptake. The structure of BT1043 complexed with N-acetyllactosamine revealed that recognition is mediated via hydrogen bonding interactions with the reducing end of beta-N-acetylglucosamine, suggesting a role in binding glycans liberated from the mucin polypeptide. The glycan-binding pocket of BT1043 suggests that binding of ligands to BT1043 relies more upon interactions with the composite sugar residues than upon overall ligand conformation as previously observed for SusD. The diversity in amino acid sequence level likely reflects early divergence from a common ancestor, while the unique and conserved alpha-helical fold the SusD family suggests a similar function in glycan uptake.

References associated with 8.A.46 family:

Bakolitsa, C., Q. Xu, C.L. Rife, P. Abdubek, T. Astakhova, H.L. Axelrod, D. Carlton, C. Chen, H.J. Chiu, T. Clayton, D. Das, M.C. Deller, L. Duan, K. Ellrott, C.L. Farr, J. Feuerhelm, J.C. Grant, A. Grzechnik, G.W. Han, L. Jaroszewski, K.K. Jin, H.E. Klock, M.W. Knuth, P. Kozbial, S.S. Krishna, A. Kumar, W.W. Lam, D. Marciano, D. McMullan, M.D. Miller, A.T. Morse, E. Nigoghossian, A. Nopakun, L. Okach, C. Puckett, R. Reyes, H.J. Tien, C.B. Trame, H. van den Bedem, D. Weekes, K.O. Hodgson, J. Wooley, M.A. Elsliger, A.M. Deacon, A. Godzik, S.A. Lesley, and I.A. Wilson. (2010). Structure of BT_3984, a member of the SusD/RagB family of nutrient-binding molecules. Acta Crystallogr Sect F Struct Biol Cryst Commun 66: 1274-1280. 20944222
Cho, K.H. and A.A. Salyers. (2001). Biochemical analysis of interactions between outer membrane proteins that contribute to starch utilization by Bacteroides thetaiotaomicron. J. Bacteriol. 183: 7224-7230. 11717282
Goulas, T., I.G. Ferrer, J.A. Hutcherson, B.A. Potempa, J. Potempa, D.A. Scott, and F.X. Gomis-RĂ¼th. (2015). Structure of RagB, a major immunodominant outer-membrane surface receptor antigen of Porphyromonas gingivalis. Mol Oral Microbiol. [Epub: Ahead of Print] 26441291
Koropatkin, N., E.C. Martens, J.I. Gordon, and T.J. Smith. (2009). Structure of a SusD homologue, BT1043, involved in mucin O-glycan utilization in a prominent human gut symbiont. Biochemistry 48: 1532-1542. 19191477
Phansopa C., Roy S., Rafferty JB., Douglas CW., Pandhal J., Wright PC., Kelly DJ. and Stafford GP. (2014). Structural and functional characterization of NanU, a novel high-affinity sialic acid-inducible binding protein of oral and gut-dwelling Bacteroidetes species. Biochem J. 458(3):499-511. 24351045
Reeves, A.R., G.R. Wang, and A.A. Salyers. (1997). Characterization of four outer membrane proteins that play a role in utilization of starch by Bacteroides thetaiotaomicron. J. Bacteriol. 179: 643-649. 9006015
Shipman, J.A., J.E. Berleman, and A.A. Salyers. (2000). Characterization of four outer membrane proteins involved in binding starch to the cell surface of Bacteroides thetaiotaomicron. J. Bacteriol. 182: 5365-5372. 10986238