View source for 1h73

[[Image:1h73.gif|left|200px]]<br /><applet load="1h73" size="350" color="white" frame="true" align="right" spinBox="true" 
caption="1h73, resolution 2.0&Aring;" />
'''CRYSTAL STRUCTURE OF HOMOSERINE KINASE COMPLEXED WITH THREONINE'''<br />

==Overview==
Homoserine kinase (HSK), the fourth enzyme in the aspartate pathway of, amino acid biosynthesis, catalyzes the phosphorylation of L-homoserine, (Hse) to L-homoserine phosphate, an intermediate in the production of, L-threonine, L-isoleucine, and in higher plants, L-methionine. The, high-resolution structures of Methanococcus jannaschii HSK ternary, complexes with its amino acid substrate and ATP analogues have been, determined by X-ray crystallography. These structures reveal the, structural determinants of the tight and highly specific binding of Hse, which is coupled with local conformational changes that enforce the, sequestration of the substrate. The delta-hydroxyl group of bound Hse is, only 3.4 A away from the gamma-phosphate of the bound nucleotide, poised, for the in-line attack at the gamma-phosphorus. The bound nucleotides are, flexible at the triphosphate tail. Nevertheless, a Mg(2+) was located in, one of the complexes that binds between the beta- and gamma-phosphates of, the nucleotide with good ligand geometry and is coordinated by the side, chain of Glu130. No strong nucleophile (base) can be located near the, phosphoryl acceptor hydroxyl group. Therefore, we propose that the, catalytic mechanism of HSK does not involve a catalytic base for, activating the phosphoryl acceptor hydroxyl but instead is mediated via a, transition state stabilization mechanism.

==About this Structure==
1H73 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Methanocaldococcus_jannaschii Methanocaldococcus jannaschii] with <scene name='pdbligand=THR:'>THR</scene> and <scene name='pdbligand=ANP:'>ANP</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Homoserine_kinase Homoserine kinase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.7.1.39 2.7.1.39] Known structural/functional Sites: <scene name='pdbsite=ANP:Anp+Binding+Site+For+Chain+A'>ANP</scene> and <scene name='pdbsite=THR:THR+Binding+Site+For+Chain+A'>THR</scene>. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1H73 OCA]. 

==Reference==
Structural basis for the catalysis and substrate specificity of homoserine kinase., Krishna SS, Zhou T, Daugherty M, Osterman A, Zhang H, Biochemistry. 2001 Sep 11;40(36):10810-8. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=11535056 11535056]
[[Category: Homoserine kinase]]
[[Category: Methanocaldococcus jannaschii]]
[[Category: Single protein]]
[[Category: Daugherty, M.]]
[[Category: Krishna, S.S.]]
[[Category: Osterman, A.L.]]
[[Category: Zhang, H.]]
[[Category: Zhou, T.]]
[[Category: ANP]]
[[Category: THR]]
[[Category: kinase]]
[[Category: threonine biosynthesis]]
[[Category: transferase]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Feb  3 09:47:13 2008''