Alpha-lactalbumin

LALBA
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 4L41, 1A4V, 1B9O, 1CB3, 1HML, 3B0I, 3B0O
Identifiers
Aliases	LALBA, entrez:3906, LYZG, lactalbumin alpha
External IDs	OMIM: 149750 MGI: 96742 HomoloGene: 1720 GeneCards: LALBA
Gene location (Human) Chr. Chromosome 12 (human)[1] Band 12q13.11 Start 48,567,684 bp[1] End 48,570,066 bp[1]
Gene location (Mouse) Chr. Chromosome 15 (mouse)[2] Band 15|15 F1 Start 98,378,281 bp[2] End 98,380,602 bp[2]
RNA expression pattern Bgee Top expressed in testicle pancreas substantia nigra spinal cord uterus organ system More reference expression data BioGPS More reference expression data
Gene ontology Molecular function calcium ion binding metal ion binding lactose synthase activity lysozyme activity Cellular component extracellular region Golgi lumen Golgi membrane extracellular space Biological process apoptotic process signal transduction defense response to bacterium cell-cell signaling lactose biosynthetic process cell wall macromolecule catabolic process GO:0051636 defense response to Gram-negative bacterium GO:0051637 defense response to Gram-positive bacterium Sources:Amigo / QuickGO
Orthologs
Species	Human	Mouse
Entrez	3906	16770
Ensembl	ENSG00000167531	ENSMUSG00000022991
UniProt	P00709	P29752
RefSeq (mRNA)	NM_002289 NM_001384350	NM_010679
RefSeq (protein)	NP_002280	NP_034809
Location (UCSC)	Chr 12: 48.57 – 48.57 Mb	Chr 15: 98.38 – 98.38 Mb
PubMed search	[3]	[4]
Wikidata
View/Edit Human View/Edit Mouse

Lactalbumin, alpha-, also known as LALBA, is a protein that in humans is encoded by the LALBA gene.^[5][6][7]

Function[]

α-Lactalbumin is a protein that regulates the production of lactose in the milk of almost all mammalian species.^[8] In primates, alpha-lactalbumin expression is upregulated in response to the hormone prolactin and increases the production of lactose.^[9]

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.^[5] The corresponding folding dynamics of alpha-lactalbumin is thus highly unusual.^[10]

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[]

The structure of alpha-lactalbumin is well known and is composed of 123 amino acids and 4 disulfide bridges. 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[]

The sequence comparison of α-lactalbumin shows a strong similarity to that of lysozymes, specifically the Ca²⁺-binding c-lysozyme.^[11] So the expected evolutionary history is that gene duplication of the c-lysozyme was followed by mutation.^[8] This gene predates the last common ancestor of mammals and birds, which probably puts its origin at about 300 Ma.^[12]

References[]

Further reading[]

External links[]

• alpha-Lactalbumin at the US National Library of Medicine Medical Subject Headings (MeSH)
• Human LALBA genome location and LALBA gene details page in the UCSC Genome Browser.