title: Structural features underlying the selective cleavage of a novel exo-type maltose-forming amylase from Pyrococcus sp. ST04.
abstract: A novel maltose-forming α-amylase (PSMA) was recently found in the hyperthermophilic archaeon Pyrococcus sp. ST04. This enzyme shows <13% amino-acid sequence identity to other known α-amylases and displays a unique enzymatic property in that it hydrolyzes both α-1,4-glucosidic and α-1,6-glucosidic linkages of substrates, recognizing only maltose units, in an exo-type manner. Here, the crystal structure of PSMA at a resolution of 1.8 Å is reported, showing a tight ring-shaped tetramer with monomers composed of two domains: an N-domain (amino acids 1-341) with a typical GH57 family (β/α)7-barrel fold and a C-domain (amino acids 342-597) composed of α-helical bundles. A small closed cavity observed in proximity to the catalytic residues Glu153 and Asp253 at the domain interface has the appropriate volume and geometry to bind a maltose unit, accounting for the selective exo-type maltose hydrolysis of the enzyme. A narrow gate at the putative subsite +1 formed by residue Phe218 and Phe452 is essential for specific cleavage of glucosidic bonds. The closed cavity at the active site is connected to a short substrate-binding channel that extends to the central hole of the tetramer, exhibiting a geometry that is significantly different from classical maltogenic amylases or β-amylases. The structural features of this novel exo-type maltose-forming α-amylase provide a molecular basis for its unique enzymatic characteristics and for its potential use in industrial applications and protein engineering.
authors.affiliation: Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon 305-806, Republic of Korea.
authors.forename: Kwang-Hyun
authors.initials: KH
authors.lastname: Park
authors.affiliation: Graduate School of Biotechnology and Institute of Life Science and Resources, Kyung Hee University, Yongin 446-701, Republic of Korea.
authors.forename: Jong-Hyun
authors.initials: JH
authors.lastname: Jung
authors.affiliation: Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon 305-806, Republic of Korea.
authors.forename: Sung-Goo
authors.initials: SG
authors.lastname: Park
authors.affiliation: Graduate School of Biotechnology and Institute of Life Science and Resources, Kyung Hee University, Yongin 446-701, Republic of Korea.
authors.forename: Myeong-Eun
authors.initials: ME
authors.lastname: Lee
authors.affiliation: Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: James F
authors.initials: JF
authors.lastname: Holden
authors.affiliation: Graduate School of Biotechnology and Institute of Life Science and Resources, Kyung Hee University, Yongin 446-701, Republic of Korea.
authors.forename: Cheon-Seok
authors.initials: CS
authors.lastname: Park
authors.affiliation: Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon 305-806, Republic of Korea.
authors.forename: Eui-Jeon
authors.initials: EJ
authors.lastname: Woo
mesh_terms: D000681:Amylases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D008320:Maltose / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D059748:Proteolysis; D019711:Pyrococcus / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D008320:Maltose; D000681:Amylases
keywords: Pyrococcus sp. ST04; exo-type hydrolase; glycoside hydrolase family 57; maltose-forming α-amylase