Crystal structure of bacterial cell-surface alginate-binding protein with an M75 peptidase motif.
A gram-negative Sphingomonas sp. A1 directly incorporates alginate polysaccharide into the cytoplasm via the cell-surface pit and ABC transporter. A cell-surface alginate-binding protein, Algp7, functions as a concentrator of the polysaccharide in the pit. Based on the primary structure and genetic organization in the bacterial genome, Algp7 was found to be homologous to an M75 peptidase motif-containing EfeO, a component of a ferrous ion transporter. Despite the presence of an M75 peptidase motif with high similarity, the Algp7 protein purified from recombinant Escherichia coli cells was inert on insulin B chain and N-benzoyl-Phe-Val-Arg-p-nitroanilide, both of which are substrates for a typical M75 peptidase, imelysin, from Pseudomonas aeruginosa. The X-ray crystallographic structure of Algp7 was determined at 2.10Å resolution by single-wavelength anomalous diffraction. Although a metal-binding motif, HxxE, conserved in zinc ion-dependent M75 peptidases is also found in Algp7, the crystal structure of Algp7 contains no metal even at the motif. The protein consists of two structurally similar up-and-down helical bundles as the basic scaffold. A deep cleft between the bundles is sufficiently large to accommodate macromolecules such as alginate polysaccharide. This is the first structural report on a bacterial cell-surface alginate-binding protein with an M75 peptidase motif.
Laboratory of Basic and Applied Molecular Biotechnology, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan.
Yukie
Y
Maruyama
Akihito
A
Ochiai
Bunzo
B
Mikami
Wataru
W
Hashimoto
Kousaku
K
Murata
D000464:Alginates / Q000737:chemistry*; D020816:Amino Acid Motifs; D018360:Crystallography, X-Ray; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D008670:Metals / Q000737:chemistry; D005810:Multigene Family; D010447:Peptide Hydrolases / Q000737:chemistry* / Q000235:genetics; D017433:Protein Structure, Secondary; D020578:Sphingomonas / Q000201:enzymology* / Q000235:genetics
D000464:Alginates; D008565:Membrane Proteins; D008670:Metals; D010447:Peptide Hydrolases