Document Detail


Structural analysis of threonine 342 mutants of soybean beta-amylase: role of a conformational change of the inner loop in the catalytic mechanism.
MedLine Citation:
PMID:  15794648     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Two different conformations of the inner loop (residues 340-346) have been found in the soybean beta-amylase structures. In the "product form", the Thr 342 residue creates hydrogen bonds with Glu 186 (catalytic acid) and with the glucose residues at subsites -1 and +1, whereas most of those interactions are lost in the "apo form". To elucidate the relationship between the structural states of the inner loop and the catalytic mechanism, Thr 342 was mutated to Val, Ser, and Ala, respectively, and their crystal structures complexed with maltose were determined together with that of the apo enzyme at 1.27-1.64 A resolutions. The k(cat) values of the T342V, T342S, and T342A mutants decreased by 13-, 360-, and 1700-fold, respectively, compared to that of the wild-type enzyme. Whereas the inner loops in the wild-type/maltose and T342V/maltose complexes adopted the product form, those of the T342S/maltose and T342A/maltose complexes showed the apo form. Structural analyses suggested that the side chain of Thr 342 in product form plays an important role in distorting the sugar ring at subsite -1, stabilizing the deprotonated form of Glu 186, and grasping the glucose residue of the remaining substrate at subsite +1. The third hypothesis was proved by the fact that T342V hydrolyzes maltoheptaose following only multichain attack in contrast to multiple attack of the wild-type enzyme.
Authors:
You-Na Kang; Aiko Tanabe; Motoyasu Adachi; Shigeru Utsumi; Bunzo Mikami
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Biochemistry     Volume:  44     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  2005 Apr 
Date Detail:
Created Date:  2005-03-29     Completed Date:  2005-05-25     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  United States    
Other Details:
Languages:  eng     Pagination:  5106-16     Citation Subset:  IM    
Affiliation:
Laboratory of Food Quality Design and Development, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan.
Data Bank Information
Bank Name/Acc. No.:
PDB/1BTC;  1BYA;  1BYB;  1BYC;  1BYD;  1WDP;  1WDQ;  1WDR;  1WDS
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MeSH Terms
Descriptor/Qualifier:
Amino Acid Sequence
Amino Acid Substitution
Catalytic Domain
Crystallography, X-Ray
Hydrogen Bonding
Kinetics
Ligands
Maltose / chemistry,  metabolism
Models, Molecular
Multiprotein Complexes
Mutagenesis, Site-Directed
Mutation*
Protein Conformation
Recombinant Proteins / chemistry,  genetics,  metabolism
Sequence Homology, Amino Acid
Soybeans / enzymology*,  genetics*
Static Electricity
Threonine / chemistry
beta-Amylase / chemistry*,  genetics*,  metabolism
Chemical
Reg. No./Substance:
0/Ligands; 0/Multiprotein Complexes; 0/Recombinant Proteins; 69-79-4/Maltose; 72-19-5/Threonine; EC 3.2.1.2/beta-Amylase

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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