Open AccessStructural characteristics of alkaline phosphatase from the moderately halophilic bacterium Halomonas sp. 593
Author(s) -
Arai Shigeki,
Yonezawa Yasushi,
Ishibashi Matsujiro,
Matsumoto Fumiko,
Adachi Motoyasu,
Tamada Taro,
Tokunaga Hiroko,
Blaber Michael,
Tokunaga Masao,
Kuroki Ryota
Publication year - 2014
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s1399004713033609
Subject(s) - halophile , halomonas , dimer , monomer , chemistry , crystallography , hydrolase , stereochemistry , hydrolysis , protein secondary structure , bacteria , biochemistry , biology , enzyme , organic chemistry , genetics , polymer
Alkaline phosphatase (AP) from the moderate halophilic bacterium Halomonas sp. 593 (HaAP) catalyzes the hydrolysis of phosphomonoesters over a wide salt‐concentration range (1–4 M NaCl). In order to clarify the structural basis of its halophilic characteristics and its wide‐range adaptation to salt concentration, the tertiary structure of HaAP was determined by X‐ray crystallography to 2.1 Å resolution. The unit cell of HaAP contained one dimer unit corresponding to the biological unit. The monomer structure of HaAP contains a domain comprised of an 11‐stranded β‐sheet core with 19 surrounding α‐helices similar to those of APs from other species, and a unique `crown' domain containing an extended `arm' structure that participates in formation of a hydrophobic cluster at the entrance to the substrate‐binding site. The HaAP structure also displays a unique distribution of negatively charged residues and hydrophobic residues in comparison to other known AP structures. AP from Vibrio sp. G15‐21 (VAP; a slight halophile) has the highest similarity in sequence (70.0% identity) and structure (C α r.m.s.d. of 0.82 Å for the monomer) to HaAP. The surface of the HaAP dimer is substantially more acidic than that of the VAP dimer (144 exposed Asp/Glu residues versus 114, respectively), and thus may enable the solubility of HaAP under high‐salt conditions. Conversely, the monomer unit of HaAP formed a substantially larger hydrophobic interior comprising 329 C atoms from completely buried residues, whereas that of VAP comprised 264 C atoms, which may maintain the stability of HaAP under low‐salt conditions. These characteristics of HaAP may be responsible for its unique functional adaptation permitting activity over a wide range of salt concentrations.