CONFORMATIONAL TRANSITION OF FRUCTOSE-1,6-BISPHOSPHATASE - STRUCTURE COMPARISON BETWEEN THE AMP COMPLEX (T-FORM) AND THE FRUCTOSE 6-PHOSPHATE COMPLEX (R-FORM)

被引:89
作者
KE, HM [1 ]
LIANG, JY [1 ]
ZHANG, YP [1 ]
LIPSCOMB, WN [1 ]
机构
[1] HARVARD UNIV,GIBBS CHEM LAB,12 OXFORD ST,CAMBRIDGE,MA 02138
关键词
D O I
10.1021/bi00232a007
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
A structure of the neutral form of fructose-1,6-bisphosphatase complexed with AMP has been determined by the molecular replacement method and refined at a 2.5-angstrom resolution to a crystallographic R factor of 0.169. The root-mean-square errors of the structure from standard geometry are 0.013 angstrom for bond lengths and 2.99-degrees for bond angles. Comparison of the AMP complex with the F6P complex shows that dimer C3-C4 twists about 19-degrees about a molecular 2-fold axis when dimers C1-C2 of the R and T forms of the enzyme are superimposed one another and that a slight shift of about 1 angstrom of the AMP domain partially compensates this twist. The R to T transition of the enzyme does not significantly change the conformation of the F6P-binding site. However, residues at the divalent metal site and the AMP site show significant positional shifts. If these results can be extended to substrate in place of F6P, they suggest that regulation of the enzyme by AMP may occur partly through effects on metal-ion affinity or position. AMP binds to the same sites of the T and R forms, but only half-occupancy was observed in the alkaline R form. Sequential binding of AMP, at least in pairs, is suggested as the unligated R form is converted to the T form. Two possible pathways are suggested for allosteric communication over about 28 angstrom between the AMP site and the active site: one via helices H1, H2, and H3 and another via the eight-stranded beta-sheet. In the former case, the loop of residues 54-68, which joins helices H2 and H3, may play an important role in the allosteric inhibition, compatible with the kinetic observation that the AMP inhibition is decreased or completely lost by proteolytic cleavages in the loop. Careful inspection of the interchain interfaces reveals that a few residues at the interface between dimers may be critical to lock the enzyme in either a T or R form.
引用
收藏
页码:4412 / 4420
页数:9
相关论文
共 33 条