PDBsum entry 1udp

Isomerase

PDB id: 1udp

Contents

Protein chains

338 a.a.*

* C-alpha coords only

Superseded by:

2udp 2udp

PDB id:

1udp

Name:

Isomerase

Structure:

Uridine diphosphogalactose 4-epimerase

Source:

(Escherichia coli)

Biol. unit:

Dimer (from PQS)

Authors:

H.M.Holden,P.A.Frey,I.Rayment

Key ref:

A.J.Bauer et al. (1992). The molecular structure of UDP-galactose 4-epimerase from Escherichia coli determined at 2.5 A resolution. Proteins, 12, 372-381. PubMed id: 1579570

Date:

20-Jul-92 Release date: 31-Oct-93

Protein chains

No UniProt id for this chain

Struc: 338 a.a.

Key reference

Proteins 12:372-381 (1992)

PubMed id: 1579570

The molecular structure of UDP-galactose 4-epimerase from Escherichia coli determined at 2.5 A resolution.

A.J.Bauer, I.Rayment, P.A.Frey, H.M.Holden.

ABSTRACT

UDP-galactose 4-epimerase catalyzes the conversion of UDP-galactose to UDP-glucose during normal galactose metabolism. The molecular structure of UDP-galactose 4-epimerase from Escherichia coli has now been solved to a nominal resolution of 2.5 A. As isolated from E. coli, the molecule is a dimer of chemically identical subunits with a total molecular weight of 79,000. Crystals of the enzyme used for this investigation were grown as a complex with the substrate analogue, UDP-benzene, and belonged to the space group P2(1)2(1)2(1) with unit cell dimensions of a = 76.3 A, b = 83.1 A, c = 132.1 A, and one dimer per asymmetric unit. An interpretable electron density map calculated to 2.5 A resolution was obtained by a combination of multiple isomorphous replacement with six heavy atom derivatives, molecular averaging, and solvent flattening. Each subunit of epimerase is divided into two domains. The larger N-terminal domain, composed of amino acid residues 1-180, shows a classic NAD+ binding motif with seven strands of parallel beta-pleated sheet flanked on either side of alpha-helices. The seventh strand of the beta-pleated sheet is contributed by amino acid residues from the smaller domain. In addition, this smaller C-terminal domain, consisting of amino acid residues 181-338, contains three strands of beta-pleated sheet, two major alpha-helices and one helical turn. The substrate analogue, UDP-benzene, binds in the cleft located between the two domains with its phenyl ring in close proximity to the nicotinamide ring of NAD+. Contrary to the extensive biochemical literature suggesting that epimerase binds only one NAD+ per functional dimer, the map clearly shows electron density for two nicotinamide cofactors binding in symmetry-related positions in the dimer. Likewise, each subunit in the dimer also binds one substrate analogue.