Abstract
Background: The regulation of milk lactose biosynthesis is highly dependent on the action of a specifier protein, α-lactalbumin (LA). Together with a glycosyltransferase, LA forms the enzyme complex lactose synthase. LA promotes the binding of glucose to the complex and facilitates the biosynthesis of lactose. To gain further insight into the molecular basis of LA funcion in lactose synthase we have determined the structures of three species variants of LA. Results: The crystal structures of guinea-pig, goat and a recombinant form of bovine LA have been determined using molecular replacement techniques. Overall, the structures are very similar and reflect their high degree of amino acid sequence identity (66-94%). Nonetheless, the structures show that a portion of the molecule (residues 105-110), known to be important for function, exhibits a variety of distinct conformers. This region lies adjacent to two residues (Phe31 and His32) that have been implicated in monosaccharide binding by lactose synthase and its conformation has significant effects on the enviroments of these functional groups. The crystal structures also demonstrate that residues currently implicated in LA's modulatory properties are located in a region of the struture that has relatively high thermal parameters and is therefore probably flexible in vivo. Conclusions: LA's proposed interaction site for the catalytic component of the lactose synthase complex is primarily located in the flexible C-terminal portion of the molecule. This general observation implies that conformational adjustments may be important for the formation and function of lactose synthase.
Original language | English |
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Pages (from-to) | 691-703 |
Number of pages | 13 |
Journal | Structure |
Volume | 4 |
Issue number | 6 |
DOIs | |
Publication status | Published - 1 Jan 1996 |
Funding
We thank Christopher Dobson and Andrei Alexandrescu of Oxford University for the generous gift of pure guinea-pig milk LA, Tassos Papageorgiou and Demetres Leonidas for help with synchrotron data collection and the staff at the Synchrotron Radiation Source (CLRC Laboratory, Daresbury) for their technical assistance. This work was supported by a Wellcome Trust prize studentship to ACWP, Leverhulme Trust and Nuffield Foundation grants to KRA, NIH grant GM21363 to KB and a NATO travel grant to KRA and KB. Keith Brew, Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Miami, FL 33101, USA. Present address for Ashley CW Pike: Department of Chemistry, University of York, Heslington, York Y01 5DD, UK. E-mail address for K Ravi Acharya (corresponding author): [email protected]
Keywords
- Conformational flexibility
- Galactosyltransferase
- Lactose synthase
- X-ray crystallography
- α-lactalbumin
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology