The crystal structures of the psychrophilic subtilisin S41 and the mesophilic subtilisin Sph reveal the same calcium-loaded state

Orna Almog*, Ana González, Noa Godin, Marina De Leeuw, Marlene J. Mekel, Daniela Klein, Sergei Braun, Gil Shoham, Richard L. Walter

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

34 Scopus citations

Abstract

We determine and compare the crystal structure of two proteases belonging to the subtilisin superfamily: S41, a cold-adapted serine protease produced by Antarctic bacilli, at 1.4 Å resolution and Sph, a mesophilic serine protease produced by Bacillus sphaericus, at 0.8 Å resolution. The purpose of this comparison was to find out whether multiple calcium ion binding is a molecular factor responsible for the adaptation of S41 to extreme low temperatures. We find that these two subtilisins have the same subtilisin fold with a root mean square between the two structures of 0.54 Å. The final models for S41 and Sph include a calcium- loaded state of five ions bound to each of these two subtilisin molecules. None of these calcium-binding sites correlate with the high affinity known binding site (site A) found for other subtilisins. Structural analysis of the five calcium-binding sites found in these two crystal structures indicate that three of the binding sites have two side chains of an acidic residue coordinating the calcium ion, whereas the other two binding sites have either a main-chain carbonyl, or only one acidic residue side chain coordinating the calcium ion. Thus, we conclude that three of the sites are of high affinity toward calcium ions, whereas the other two are of low affinity. Because Sph is a mesophilic subtilisin and S41 is a psychrophilic subtilisin, but both crystal structures were found to bind five calcium ions, we suggest that multiple calcium ion binding is not responsible for the adaptation of S41 to low temperatures.

Original languageAmerican English
Pages (from-to)489-496
Number of pages8
JournalProteins: Structure, Function and Bioinformatics
Volume74
Issue number2
DOIs
StatePublished - 1 Feb 2009

Keywords

  • Calcium-binding
  • Cold adaptation
  • Crystal structure
  • Mesophilic
  • Psychrophilic
  • Serine protease
  • Subtilisin
  • Ultrahigh resolution

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