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![[Figure 6]](cb5114fig6mag.jpg)
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Figure 6
(a, b) The mode of binding of Neu5Ac and Neu5Gc in the active site of VcCMAS. The electrostatic surface-potential map shows that the hydrophobic residues Phe133, Tyr166, Tyr183, Phe196 and Pro197 constitute the molecular environment around the C5 N-acetyl group of Neu5Ac or Neu5Gc. (c) A structural comparison of the sialic acid binding pocket between the prokaryotic [NmCMAS (PDB entry 1eyr) and VcCMAS (PDB entry 6ifd)] and eukaryotic (murine CMAS; PDB entry 1qwj) enzymes is shown. Superimposition of all three structures suggests that the loop that harbors the hydrophobic residues (Phe192 and Phe193; NmCMAS nomenclature) differs both in position and in amino-acid sequence. The VcCMAS structure is shown in a cartoon representation in green, NmCMAS in blue and murine CMAS in orange, and residues in the hydrophobic pocket are shown in stick representation. (d) A structure-based sequence alignment using Expresso (Armougom et al., 2006  ) shows much lower conservation of the dimerization domain across bacterial and eukaryotic species. Residues (Phe133, Tyr166, Tyr183, Phe196 and Pro197; VcCMAS nomenclature) located close to the C5 N-acetyl moiety of sialic acid are marked with blue rectangles. The CMAS sequences from N. meningitidis, P. multocida, P. haemolytica, C. thermocellum, E. coli, H. ducreyi, S. agalactiae, mouse and human were used in this alignment |
![[Figure 6]](cb5114fig6.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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