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Role of lysine versus arginine in enzyme cold-adaptation: modifying lysine to homo-arginine stabilizes the cold-adapted α-amylase from Pseudoalteramonas haloplanktis
Siddiqui, K.S.; Poljak, A.; Guilhaus, M.; De Francisci, D.; Curmi, P.M.G.; Feller, G.; D'Amico, S.; Gerday, C.; Uversky, V.N.; Cavicchioli, R. (2006). Role of lysine versus arginine in enzyme cold-adaptation: modifying lysine to homo-arginine stabilizes the cold-adapted α-amylase from Pseudoalteramonas haloplanktis. Proteins-Structure Function and Bioinformatics 64(2): 486-501. dx.doi.org/10.1002/prot.20989
In: Proteins-Structure Function and Bioinformatics. Wiley-Blackwell: Hoboken. ISSN 0887-3585, more
Peer reviewed article  

Available in Authors 

Keyword
    Marine
Author keywords
    psychrophilic; guanidination; structure-function-stability relationship;enzyme kinetics; thermodynamics; bioinformatics

Authors  Top 
  • Siddiqui, K.S.
  • Poljak, A.
  • Guilhaus, M.
  • De Francisci, D.
  • Curmi, P.M.G.
  • Feller, G., more
  • D'Amico, S., more
  • Gerday, C., more
  • Uversky, V.N.
  • Cavicchioli, R.

Abstract
    The cold-adapted α-amylase from Pseudoalteromonas haloplanktis (AHA) is a multidomain enzyme capable of reversible unfolding. Cold-adapted proteins, including AHA, have been predicted to be structurally flexible and conformationally unstable as a consequence of a high lysine-to-arginine ratio. In order to examine the role of low arginine content in structural flexibility of AHA, the amino groups of lysine were guanidinated to form homo-arginine (hR), and the structure–function–stability properties of the modified enzyme were analyzed by transverse urea gradient-gel electrophoresis. The extent of modification was monitored by MALDI-TOF-MS, and correlated to changes in activity and stability. Modifying lysine to hR produced a conformationally more stable and less active α-amylase. The kcat of the modified enzyme decreased with a concomitant increase in ΔH# and decrease in Km. To interpret the structural basis of the kinetic and thermodynamic properties, the hR residues were modeled in the AHA X-ray structure and compared to the X-ray structure of a thermostable homolog. The experimental properties of the modified AHA were consistent with K106hR forming an intra-Domain B salt bridge to stabilize the active site and decrease the cooperativity of unfolding. Homo-Arg modification also appeared to alter Ca2+ and Cl binding in the active site. Our results indicate that replacing lysine with hR generates mesophilic-like characteristics in AHA, and provides support for the importance of lysine residues in promoting enzyme cold adaptation. These data were consistent with computational analyses that show that AHA possesses a compositional bias that favors decreased conformational stability and increased flexibility.

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