type	Journal Article
authors	Kielkopf, C. L.; Burley, S. K.
title	X-ray structures of threonine aldolase complexes: Structural basis of substrate recognition
journal	Biochemistry
Activity	4.1.2.5
Family	4.1.2.5
sel	selected
ui	12269813
year	(2002)
volume	41
number	39
pages	11711-20
abstract	L-Threonine acetaldehyde-lyase (threonine aldolase, TA) is a pyridoxal- 5'-phosphate-dependent (PLP) enzyme that catalyzes conversion of L- threonine or L-allo-threonine to glycine and acetaldehyde in a secondary glycine biosynthetic pathway. X-ray structures of Thermatoga maritima TA have been determined as the apo-enzyme at 1.8 A resolution and bound to substrate L-allo-threonine and product glycine at 1.9 and 2.0 A resolution, respectively. Despite low pairwise sequence identities, TA is a member of aspartate aminotransferase (AATase) fold family of PLP enzymes. The enzyme forms a 222 homotetramer with the PLP cofactor bound via a Schiff-base linkage to Lys199 within a domain interface. The structure reveals bound calcium and chloride ions that appear to contribute to catalysis and oligomerization, respectively. Although L-threonine and L-allo-threonine are substrates for T. maritima TA, enzymatic assays revealed a strong preference for L-allo- threonine. Structures of the external aldimines with substrate/product reveal a pair of histidines that may provide flexibility in substrate recognition. Variation in the threonine binding pocket may explain preferences for L-allo-threonine versus L-threonine among TA family members.
last changed	2009/06/19 13:24