Isozyme hybrids within the protruding third loop domain of the barley alpha-amylase (beta/alpha)8-barrel. Implication for BASI sensitivity and substrate affinity.
Barley alpha-amylase isozymes AMY1 and AMY2 contain three structural domains: a catalytic (beta/alpha)8-barrel (domain A) with a protruding loop (domain B; residues 89-152) that binds Ca2+, and a small C-terminal domain. Different parts of domain B secure isozyme specific properties as identified for three AMY1-AMY2 hybrids, obtained by homeologous recombination in yeast, with crossing-over at residues 112, 116, and 144. The AMY1 regions Val90-Thr112 and Ala145-Leu161 thus confer high affinities for the substrates alpha-D-maltoheptaoside and amylose, respectively. Leu117-Phe144, and to a lesser degree Ala145-Leu161, are critical for the stability at low pH characteristic of AMY1 and for the sensitivity to barley alpha-amylase/subtilisin inhibitor specific to AMY2.
Juge
N
N
Carlsberg Laboratory, Department of Chemistry, Copenhagen, Denmark.
Rodenburg
K W
KW
Guo
X J
XJ
Chaix
J C
JC
Svensson
B
B
D000595:Amino Acid Sequence; D001467:Hordeum / Q000201:enzymology*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D000516:alpha-Amylases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*
D007527:Isoenzymes; D000516:alpha-Amylases