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| [[Image:1nkh.gif|left|200px]] | | [[Image:1nkh.png|left|200px]] |
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| ==Overview==
| | {{ABSTRACT_11419947}} |
| The lactose synthase (LS) enzyme is a 1:1 complex of a catalytic component, beta1,4-galactosyltransferse (beta4Gal-T1) and a regulatory component, alpha-lactalbumin (LA), a mammary gland-specific protein. LA promotes the binding of glucose (Glc) to beta4Gal-T1, thereby altering its sugar acceptor specificity from N-acetylglucosamine (GlcNAc) to glucose, which enables LS to synthesize lactose, the major carbohydrate component of milk. The crystal structures of LS bound with various substrates were solved at 2 A resolution. These structures reveal that upon substrate binding to beta4Gal-T1, a large conformational change occurs in the region comprising residues 345 to 365. This repositions His347 in such a way that it can participate in the coordination of a metal ion, and creates a sugar and LA-binding site. At the sugar-acceptor binding site, a hydrophobic N-acetyl group-binding pocket is found, formed by residues Arg359, Phe360 and Ile363. In the Glc-bound structure, this hydrophobic pocket is absent. For the binding of Glc to LS, a reorientation of the Arg359 side-chain occurs, which blocks the hydrophobic pocket and maximizes the interactions with the Glc molecule. Thus, the role of LA is to hold Glc by hydrogen bonding with the O-1 hydroxyl group in the acceptor-binding site on beta4Gal-T1, while the N-acetyl group-binding pocket in beta4Gal-T1 adjusts to maximize the interactions with the Glc molecule. This study provides details of a structural basis for the partially ordered kinetic mechanism proposed for lactose synthase.
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| ==About this Structure== | | ==About this Structure== |
| 1NKH is a [[Protein complex]] structure of sequences from [http://en.wikipedia.org/wiki/Bos_taurus Bos taurus] and [http://en.wikipedia.org/wiki/Mus_musculus Mus musculus]. This structure supersedes the now removed PDB entry [http://oca.weizmann.ac.il/oca-bin/send-pdb?obs=1&id=1j8x 1j8x]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1NKH OCA]. | | 1NKH is a [[Protein complex]] structure of sequences from [http://en.wikipedia.org/wiki/Bos_taurus Bos taurus] and [http://en.wikipedia.org/wiki/Mus_musculus Mus musculus]. This structure supersedes the now removed PDB entry [http://oca.weizmann.ac.il/oca-bin/send-pdb?obs=1&id=1j8x 1j8x]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1NKH OCA]. |
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| ==Reference==
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| Crystal structure of lactose synthase reveals a large conformational change in its catalytic component, the beta1,4-galactosyltransferase-I., Ramakrishnan B, Qasba PK, J Mol Biol. 2001 Jun 29;310(1):205-18. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/11419947 11419947]
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| [[Category: Bos taurus]] | | [[Category: Bos taurus]] |
| [[Category: Mus musculus]] | | [[Category: Mus musculus]] |
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| [[Category: Lactose synthease]] | | [[Category: Lactose synthease]] |
| [[Category: Udp and mn binding]] | | [[Category: Udp and mn binding]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 02:38:23 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed Jun 25 19:18:41 2008'' |
