CstII is a bifunctional sialyltransferase from Campylobacter jejuni that is active as a tetramer. CstIIs from different strains show substantial differences in enzyme activities (mono- versus bi-functional) and kinetic parameters. Crystal structures of CstII show that His85, conserved in CstIIs from different strains is part of an 11-residue loop that abuts the extended acceptor-binding site and is also part of the subunit interface. In this study, the role of His85 in the activity of CstII has been investigated by mutating it to Ala, Phe, Trp or Tyr. His85 is found to be essential for α2,3-sialyltransferase activity but not α2,8-sialyltransferase activity. Although no gross changes are observed in secondary and tertiary structures, thermal stability is affected by His85 mutation. MD simulations show changes in the flexibility of the loop regions including those in the binding site.
Keywords: MD simulation; bifunctional; docking; flexibility; sialyltransferase.
© The Authors 2014. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.