1cbu
From Proteopedia
|
ADENOSYLCOBINAMIDE KINASE/ADENOSYLCOBINAMIDE PHOSPHATE GUANYLYLTRANSFERASE (COBU) FROM SALMONELLA TYPHIMURIUM
Overview
The X-ray structure of adenosylcobinamide kinase/adenosylcobinamide, phosphate guanylyltransferase (CobU) from Salmonella typhimurium has been, determined to 2.3 A resolution. This enzyme of subunit molecular weight 19, 770 plays a central role in the assembly of the nucleotide loop for, adenosylcobalamin where it catalyzes both the phosphorylation of the, 1-amino-2-propanol side chain of the corrin ring and the subsequent, attachment of GMP to form the product adenosylcobinamide-GDP. The kinase, activity is believed to be associated with a P-loop motif, whereas the, transferase activity proceeds at a different site on the enzyme via a, guanylyl intermediate. The enzyme was crystallized in the space group, C2221 with unit cell dimensions of a = 96.4 A, b = 114.4 A, and c = 106.7, A, with three subunits per asymmetric unit. The structure reveals that the, enzyme is a molecular trimer and appears somewhat like a propeller with, overall molecular dimensions of approximately 64 A x 77 A x 131 A. Each, subunit consists of a single domain that is dominated by a seven-stranded, mixed beta-sheet flanked on either side by a total of five alpha-helices, and one helical turn. Six of the seven beta-strands run parallel. The, C-terminal strand lies at the edge of the sheet and runs antiparallel to, the others. Interestingly, CobU displays a remarkable structural and, topological similarity to the central domain of the RecA protein, although, the reason for this observation is unclear. The structure contains a, P-loop motif located at the base of a prominent cleft formed by the, association of two subunits and is most likely the kinase active site., Each subunit of CobU contains a cis peptide bond between Glu80 and Cys81, where Glu80 faces the P-loop and might serve to coordinate the magnesium, ion of the triphosphate substrate. Interestingly, His46, which is the, putative site for guanylylation, lies approximately 21 A from the P-loop, and is solvent-exposed. This suggests that the enzyme undergoes a, conformational change when the substrates bind to bring these two active, sites into closer proximity.
About this Structure
1CBU is a Single protein structure of sequence from Salmonella typhimurium with SO4 as ligand. Full crystallographic information is available from OCA.
Reference
Three-dimensional structure of adenosylcobinamide kinase/adenosylcobinamide phosphate guanylyltransferase from Salmonella typhimurium determined to 2.3 A resolution,., Thompson TB, Thomas MG, Escalante-Semerena JC, Rayment I, Biochemistry. 1998 May 26;37(21):7686-95. PMID:9601028
Page seeded by OCA on Tue Nov 20 12:19:40 2007
