Structure (Page 2)

The GAPDH-like, C-terminal domain contains a mainly antiparallel B-sheet that creates a mainly hydrophobic interface between two subunits (O and P - not shown). Compared to bacterial GAPDH, the nucleotide-binding domain in the SS protein is rotated 10 degrees in relation to the catalytic domain. The alpha helix (39-47) goes from the second B sheet to a short third B sheet. There are two alpha helices between the third and fourth B sheets. There is a large loop called the S-loop in the catalytic domain (169-178). The S-loop of subunit O interacts with subunits R (not shown) and Q. Most of the prolines are found in the bends and the regions that are not characterized as alpha strand or beta sheet. Prolines 178, 186, and 190 are in cis formation. The loop that contains Pro 186 and 190 are involved in contacts at the interface of subunits O and P. Alpha helix 258-268 and the following loop (269-274) make mainly salt-bridge interactions at the interface of the O and Q subunits. There are two salt-bridge clusters, including an extensive one at Lys14 at the interface of O and Q with 14 charged residues, a sulphate ion, and His 299. The salt-bridge at Lys14 is not conserved in other archaeal GAPDH. The other salt-bridge, that includes Arg146, Glu307, Arg245, and Asp310, is in the catalytic domain and is conserved in all archaeal GAPDH.

There is a disulfide bridge between Cys 123 and Cys 149, the two red colored cysteines (on each chain):

This disulfide bond is not seen in other archaeal GAPDH, but it seems to provide structural stability holding together alpha helix 138-153 of the catalytic domain and a short alpha helix 120-125 from the NAD binding domain; this may help provide thermostability. Disulfide bonds are usually uncommon in intracellular enzymes.

Complete Homotetramer

Other Related Oxidoreductases: 1cf2: d-glyceraldehyde 3-phosphate dehydrogenase from the hyperthermophilic archaeon methanothermus fervidus

CATH Domain Diagram

Predict Protein Info