PR00136

LACTALBUMIN

PRINTS entry
Member databasePRINTS
PRINTS typefamily
Short nameLACTALBUMIN

Description
Imported from IPR000545

Alpha-lactalbumin comprises 15 percent of the total human milk protein and is essential for lactose production
[1]
. It is a globular calcium-binding metalloprotein secreted in the lactating mammary gland
[2]
, the calcium being bound in a novel binding loop that is superficially similar to the classic EF-hand motif. Lactalbumin attaches to beta-galactosyltransferase on the luminal surface of the Golgi apparatus, creating the lactose synthetase complex
[1]
, which catalyses the addition of galactose to glucose, forming lactose. It has been claimed that calcium controls the release of lactalbumin from the golgi membrane and that the pattern of ion binding may also affect the catalytic properties of the lactose synthetase complex. The lactalbumin gene also contains a novel upstream regulatory sequence called the `milk box'
[3]
, which is also found in genes of other milk proteins, and may be involved in either hormone regulation or tissue-specific expression in the lactating mammary gland. Alpha-lactalbumin is similar to C-type lysozyme in terms of primary sequence and structure
[4]
, and has probably evolved from a common ancestral protein. There is, however, no similarity in function.

References
Imported from IPR000545

1.Alpha-lactalbumin possesses a novel calcium binding loop. Stuart DI, Acharya KR, Walker NP, Smith SG, Lewis M, Phillips DC. Nature 324, 84-7, (1986). View articlePMID: 3785375

2.Crystal structure of human alpha-lactalbumin at 1.7 A resolution. Acharya KR, Ren JS, Stuart DI, Phillips DC, Fenna RE. J. Mol. Biol. 221, 571-81, (1991). View articlePMID: 1920433

3.Structure and expression of the guinea-pig alpha-lactalbumin gene. Laird JE, Jack L, Hall L, Boulton AP, Parker D, Craig RK. Biochem. J. 254, 85-94, (1988). View articlePMID: 2845947

4.Evolution of alpha-lactalbumins. The complete amino acid sequence of the alpha-lactalbumin from a marsupial (Macropus rufogriseus) and corrections to regions of sequence in bovine and goat alpha-lactalbumins. Shewale JG, Sinha SK, Brew K. J. Biol. Chem. 259, 4947-56, (1984). View articlePMID: 6715332

Supplementary References

1. The calcium-binding property of equine lysozyme. Nitta K, Tsuge H, Sugai S, Shimazaki K. FEBS Lett. 223, 405-8, (1987). View articlePMID: 3666156

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