Alpha-lactalbumin

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Lactalbumin, alpha-

PDB rendering based on 1a4v.
Available structures
PDB Ortholog search: PDBe, RCSB
Identifiers
Symbols LALBA ; MGC138521; MGC138523
External IDs OMIM149750 MGI96742 HomoloGene1720 GeneCards: LALBA Gene
EC number 2.4.1.22
RNA expression pattern
PBB GE LALBA 207816 at tn.png
More reference expression data
Orthologs
Species Human Mouse
Entrez 3906 16770
Ensembl ENSG00000167531 ENSMUSG00000022991
UniProt P00709 P29752
RefSeq (mRNA) NM_002289 NM_010679
RefSeq (protein) NP_002280 NP_034809
Location (UCSC) Chr 12:
48.96 – 48.96 Mb
Chr 15:
98.48 – 98.48 Mb
PubMed search [1] [2]

Lactalbumin, alpha-, also known as LALBA, is a protein that in humans is encoded by the LALBA gene.[1][2][3]

Function[edit]

α-Lactalbumin is a protein present in the milk of almost all mammalian species.[4] In primates, alpha-lactalbumin expression is upregulated in response to the hormone prolactin and increases the production of lactose.[5]

α-Lactalbumin forms the regulatory subunit of the lactose synthase (LS) heterodimer and β-1,4-galactosyltransferase (beta4Gal-T1) forms the catalytic component. Together, these proteins enable LS to produce lactose by transferring galactose moieties to glucose. As a multimer, alpha-lactalbumin strongly binds calcium and zinc ions and may possess bactericidal or antitumor activity. A folding variant of human alpha-lactalbumin that may form in acidic environments such as the stomach, called HAMLET, probably induces apoptosis in tumor and immature cells.[1]

When formed into a complex with Gal-T1, a galactosyltransferase, α-lactalbumin, enhances the enzyme's affinity for glucose by about 1000 times, and inhibits the ability to polymerise multiple galactose units. This gives rise to a pathway for forming lactose by converting Gal-TI to Lactose synthase.

Physical properties[edit]

The molecular weight is 14178 Da, and the isoelectric point is between 4.2 and 4.5. One of the main structural differences with beta-lactoglobulin is that it does not have any free thiol group that can serve as the starting-point for a covalent aggregation reaction. As a result, pure α-lactalbumin will not form gels upon denaturation and acidification.

Evolution[edit]

The sequence comparison of α-lactalbumin shows a strong similarity to that of lysozymes, specifically the Ca2+-binding c-lysozyme.[6] So the expected evolutionary history is that gene duplication of the c-lysozyme was followed by mutation.[4] This gene predates the last common ancestor of mammals and birds, which probably puts its origin at about 300 Ma.[7]

References[edit]

  1. ^ a b "Entrez Gene: LALBA lactalbumin, alpha-". 
  2. ^ Hall L, Davies MS, Craig RK (January 1981). "The construction, identification and characterisation of plasmids containing human alpha-lactalbumin cDNA sequences". Nucleic Acids Res. 9 (1): 65–84. doi:10.1093/nar/9.1.65. PMC 326669. PMID 6163135. 
  3. ^ Hall L, Emery DC, Davies MS, Parker D, Craig RK (March 1987). "Organization and sequence of the human alpha-lactalbumin gene". Biochem. J. 242 (3): 735–42. PMC 1147772. PMID 2954544. 
  4. ^ a b Qasba PK, Kumar S (1997). "Molecular divergence of lysozymes and alpha-lactalbumin". Crit. Rev. Biochem. Mol. Biol. 32 (4): 255–306. doi:10.3109/10409239709082574. PMID 9307874. 
  5. ^ Kleinberg JL, Todd J, Babitsky G (1983). "Inhibition by estradiol of the lactogenic effect of prolactin in primate mammary tissue: reversal by antiestrogens LY 156758 and tamoxifen.". PNAS 80 (13): 4144–4148. doi:10.1073/pnas.80.13.4144. PMC 394217. PMID 6575400. 
  6. ^ Acharya KR, Stuart DI, Walker NP, Lewis M, Phillips DC (1989). "Refined structure of baboon alpha-lactalbumin at 1.7 A resolution. Comparison with C-type lysozyme". J. Mol. Biol. 208 (1): 99–127. doi:10.1016/0022-2836(89)90091-0. PMID 2769757. 
  7. ^ Prager EM, Wilson AC (1988). "Ancient origin of lactalbumin from lysozyme: analysis of DNA and amino acid sequences". J. Mol. Evol. 27 (4): 326–35. doi:10.1007/BF02101195. PMID 3146643. 

Further reading[edit]

External links[edit]