title: Correlation between catalysis and tertiary structure arrangement in an archaeal halophilic subtilase.
abstract: Nep (Natrialba magadii extracellular protease) is a halolysin-like peptidase secreted by the haloalkaliphilic archaeon N. magadii that exhibits optimal activity and stability in salt-saturated solutions. In this work, the effect of salt on the function and structure of Nep was investigated. In absence of salt, Nep became unfolded and aggregated, leading to the loss of activity. The enzyme did not recover its structural and functional properties even after restoring the ideal conditions for catalysis. At salt concentrations higher than 1 M (NaCl), Nep behaved as monomers in solution and its enzymatic activity displayed a nonlinear concave-up dependence with salt concentration resulting in a 20-fold activation at 4 M NaCl. Although transition from a high to a low-saline environment (3-1 M NaCl) did not affect its secondary structure contents, it diminished the enzyme stability and provoked large structural rearrangements, changing from an elongated shape at 3 M NaCl to a compact conformational state at 1 M NaCl. The thermodynamic analysis of peptide hydrolysis by Nep suggests a significant enzyme reorganization depending on the environmental salinity, which supports in solution SAXS and DLS studies. Moreover, solvent kinetic isotopic effect (SKIE) data indicates the general acid-base mechanism as the rate-limiting step for Nep catalysis, like classical serine-peptidases. All these data correlate the Nep conformational states with the enzymatic behavior providing a further understanding on the stability and structural determinants for the functioning of halolysins under different salinities.
authors.affiliation: Laboratório Nacional de Biociências, Centro Nacional de Pesquisas em Energia e Materiais, Giuseppe Maximo Scolfaro, 10000, Campinas 13083-970, Brazil.
authors.forename: Tatiana A C B
authors.initials: TA
authors.lastname: Souza
authors.forename: Débora N
authors.initials: DN
authors.lastname: Okamoto
authors.forename: Diego M
authors.initials: DM
authors.lastname: Ruiz
authors.forename: Lilian C G
authors.initials: LC
authors.lastname: Oliveira
authors.forename: Márcia Y
authors.initials: MY
authors.lastname: Kondo
authors.forename: Ivarne L S
authors.initials: IL
authors.lastname: Tersario
authors.forename: Luiz
authors.initials: L
authors.lastname: Juliano
authors.forename: Rosana E
authors.initials: RE
authors.lastname: De Castro
authors.forename: Iuri E
authors.initials: IE
authors.lastname: Gouvea
authors.forename: Mário T
authors.initials: MT
authors.lastname: Murakami
mesh_terms: D002384:Catalysis; D004795:Enzyme Stability; D006216:Halobacteriaceae / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D017434:Protein Structure, Tertiary; D013381:Subtilisins / Q000737:chemistry* / Q000378:metabolism*; D013696:Temperature
chemical_list: D013381:Subtilisins