Novel type of enzyme multimerization enhances substrate affinity of oat beta-glucosidase.
Oat beta-glucosidase in plastid hydrolyzes avenacosides to C26-desgluco-avenacosides to combat against fungal infections. The enzyme has a unique quaternary protein structure of a three-dimensionally radiated assembly of long fibrillae. We elucidated the fibrillar assembly of oat type 1 beta-glucosidase by means of cryo-electron microscopy, enzyme kinetics and chemical modification. It was assembled by linear stacking of hollow trimeric units and the resulting fibril had a long central tunnel connecting to the outer medium via regularly distributed side fenestrations. The enzyme active sites were located within the central tunnel. This unique multimer assembly increased enzyme affinity to avenacosides, in vivo substrates, and may function to discriminate avenacosides from many other kinds of beta-glucoside in oat. The fibrillar multimer of oat beta-glucosidase is a novel quaternary protein structure for enzyme supramolecular assembly that may have a functional role in the regulation of enzyme affinity.
Kim
Sang-Yeob
SY
Department of Genetic Engineering, College of Natural Science, Kyungpook National University, Daegu 702-701, Republic of Korea.
Kim
Yong-Woo
YW
Hegerl
Reiner
R
Cyrklaff
Marek
M
Kim
In-Soo
IS
D018554:Avena / Q000201:enzymology*; D001665:Binding Sites; D020285:Cryoelectron Microscopy; D011487:Protein Conformation; D013379:Substrate Specificity; D001617:beta-Glucosidase / Q000737:chemistry* / Q000302:isolation & purification
C087992:avenacosidase; D001617:beta-Glucosidase