title: Structural adaptation of extreme halophilic proteins through decrease of conserved hydrophobic contact surface.
abstract: BACKGROUND
  Halophiles are extremophilic microorganisms growing optimally at high salt concentrations. There are two strategies used by halophiles to maintain proper osmotic pressure in their cytoplasm: accumulation of molar concentrations of potassium and chloride with extensive adaptation of the intracellular macromolecules ("salt-in" strategy) or biosynthesis and/or accumulation of organic osmotic solutes ("osmolyte" strategy). Our work was aimed at contributing to the understanding of the shared molecular mechanisms of protein haloadaptation through a detailed and systematic comparison of a sample of several three-dimensional structures of halophilic and non-halophilic proteins. Structural differences observed between the "salt-in" and the mesophilic homologous proteins were contrasted to those observed between the "osmolyte" and mesophilic pairs.
  
  
  RESULTS
  The results suggest that haloadaptation strategy in the presence of molar salt concentration, but not of osmolytes, necessitates a weakening of the hydrophobic interactions, in particular at the level of conserved hydrophobic contacts. Weakening of these interactions counterbalances their strengthening by the presence of salts in solution and may help the structure preventing aggregation and/or loss of function in hypersaline environments.
  
  
  CONCLUSIONS
  Considering the significant increase of biotechnology applications of halophiles, the understanding of halophilicity can provide the theoretical basis for the engineering of proteins of great interest because stable at concentrations of salts that cause the denaturation or aggregation of the majority of macromolecules.
authors.affiliation: Dipartimento di Scienze Biochimiche "A, Rossi Fanelli", Università di Roma La Sapienza, 00185 Roma, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Siglioccolo
authors.forename: Alessandro
authors.initials: A
authors.lastname: Paiardini
authors.forename: Maria
authors.initials: M
authors.lastname: Piscitelli
authors.forename: Stefano
authors.initials: S
authors.lastname: Pascarella
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D019295:Computational Biology; D017124:Conserved Sequence; D004305:Dose-Response Relationship, Drug; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D011487:Protein Conformation; D012492:Salts / Q000494:pharmacology*; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D012492:Salts