J. Biol. Chem., Vol. 263, Issue 1, 150-156, 01, 1988
Preliminary crystal structure of Acinetobacter glutaminasificans glutaminase-asparaginase
HL Ammon, IT Weber, A Wlodawer, RW Harrison, GL Gilliland, KC Murphy, L Sjolin and J Roberts
Department of Chemistry and Biochemistry, University of Maryland, College Park 20742.
The preliminary structure of a glutaminase-asparaginase from Acinetobacter
glutaminasificans is reported. The structure was determined at 3.0-A
resolution with a combination of phase information from multiple
isomorphous replacement at 4-5-A resolution and phase improvement and
extension by two density modification techniques. The electron density map
was fitted by a polypeptide chain that was initially polyalanine. This was
subsequently replaced by a polypeptide with an amino acid sequence in
agreement with the sizes and shapes of the side chain electron densities.
The crystallographic R factor is 0.300 following restrained least squares
refinement with data to 2.9-A resolution. The A. glutaminasificans
glutaminase-asparaginase subunit folds into two domains: the aminoterminal
domain contains a five- stranded beta sheet surrounded by five alpha
helices, while the carboxyl-terminal domain contains three alpha helices
and less regular structure. The connectivity is not fully determined at
present, due in part to the lack of a complete amino acid sequence. The A.
glutaminasificans glutaminase-asparaginase structure has been used
successfully to determine the relative orientations of the molecules in
crystals of Pseudomonas 7A glutaminase-asparaginase, in crystals of Vibrio
succinogenes asparaginase, and in a new crystal form of Escherichia coli
asparaginase (space group 1222, one subunit per asymmetric unit).
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