ID   LALB2_HORSE             Reviewed;         123 AA.
AC   P08896;
DT   01-NOV-1988, integrated into UniProtKB/Swiss-Prot.
DT   01-NOV-1988, sequence version 1.
DT   03-AUG-2022, entry version 109.
DE   RecName: Full=Alpha-lactalbumin B/C;
DE   AltName: Full=Lactose synthase B protein;
OS   Equus caballus (Horse).
OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Mammalia;
OC   Eutheria; Laurasiatheria; Perissodactyla; Equidae; Equus.
OX   NCBI_TaxID=9796;
RN   [1]
RP   PROTEIN SEQUENCE.
RX   PubMed=3606826; DOI=10.1515/bchm3.1987.368.1.427;
RA   Godovac-Zimmermann J., Shaw D., Conti A., McKenzie H.A.;
RT   "Identification and the primary structure of equine alpha-lactalbumin B and
RT   C (Equus caballus, Perissodactyla).";
RL   Biol. Chem. Hoppe-Seyler 368:427-433(1987).
CC   -!- FUNCTION: Regulatory subunit of lactose synthase, changes the substrate
CC       specificity of galactosyltransferase in the mammary gland making
CC       glucose a good acceptor substrate for this enzyme. This enables LS to
CC       synthesize lactose, the major carbohydrate component of milk. In other
CC       tissues, galactosyltransferase transfers galactose onto the N-
CC       acetylglucosamine of the oligosaccharide chains in glycoproteins.
CC   -!- SUBUNIT: Lactose synthase (LS) is a heterodimer of a catalytic
CC       component, beta1,4-galactosyltransferase (beta4Gal-T1) and a regulatory
CC       component, alpha-lactalbumin (LA).
CC   -!- SUBCELLULAR LOCATION: Secreted.
CC   -!- TISSUE SPECIFICITY: Mammary gland specific. Secreted in milk.
CC   -!- SIMILARITY: Belongs to the glycosyl hydrolase 22 family.
CC       {ECO:0000255|PROSITE-ProRule:PRU00680}.
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DR   PIR; A26541; A26541.
DR   AlphaFoldDB; P08896; -.
DR   SMR; P08896; -.
DR   Allergome; 1498; Equ c ALA.
DR   PeptideAtlas; P08896; -.
DR   Proteomes; UP000002281; Unplaced.
DR   GO; GO:0005576; C:extracellular region; IEA:UniProtKB-SubCell.
DR   GO; GO:0005509; F:calcium ion binding; IEA:InterPro.
DR   GO; GO:0004461; F:lactose synthase activity; IEA:InterPro.
DR   GO; GO:0003796; F:lysozyme activity; IBA:GO_Central.
DR   GO; GO:0005989; P:lactose biosynthetic process; IEA:UniProtKB-KW.
DR   InterPro; IPR001916; Glyco_hydro_22.
DR   InterPro; IPR019799; Glyco_hydro_22_CS.
DR   InterPro; IPR000545; Lactalbumin.
DR   InterPro; IPR023346; Lysozyme-like_dom_sf.
DR   PANTHER; PTHR11407; PTHR11407; 1.
DR   PANTHER; PTHR11407:SF32; PTHR11407:SF32; 1.
DR   Pfam; PF00062; Lys; 1.
DR   PRINTS; PR00136; LACTALBUMIN.
DR   PRINTS; PR00135; LYZLACT.
DR   SMART; SM00263; LYZ1; 1.
DR   SUPFAM; SSF53955; SSF53955; 1.
DR   PROSITE; PS00128; GLYCOSYL_HYDROL_F22_1; 1.
DR   PROSITE; PS51348; GLYCOSYL_HYDROL_F22_2; 1.
PE   1: Evidence at protein level;
KW   Calcium; Direct protein sequencing; Disulfide bond; Lactose biosynthesis;
KW   Metal-binding; Milk protein; Reference proteome; Secreted.
FT   CHAIN           1..123
FT                   /note="Alpha-lactalbumin B/C"
FT                   /id="PRO_0000208837"
FT   DOMAIN          1..123
FT                   /note="C-type lysozyme"
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00680"
FT   BINDING         79
FT                   /ligand="Ca(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29108"
FT                   /evidence="ECO:0000250|UniProtKB:P00711"
FT   BINDING         82
FT                   /ligand="Ca(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29108"
FT                   /evidence="ECO:0000250|UniProtKB:P00711"
FT   BINDING         84
FT                   /ligand="Ca(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29108"
FT                   /evidence="ECO:0000250|UniProtKB:P00711"
FT   BINDING         87
FT                   /ligand="Ca(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29108"
FT                   /evidence="ECO:0000250|UniProtKB:P00711"
FT   BINDING         88
FT                   /ligand="Ca(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29108"
FT                   /evidence="ECO:0000250|UniProtKB:P00711"
FT   DISULFID        6..120
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00680"
FT   DISULFID        28..111
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00680"
FT   DISULFID        61..77
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00680"
FT   DISULFID        73..91
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00680"
FT   VARIANT         95
FT                   /note="D -> I (in component C)"
SQ   SEQUENCE   123 AA;  14251 MW;  75BD4128450500AC CRC64;
     KQFTKCQLSQ VLKSMDGYKG VTLPEWICTI FHNSGYDTQT IVKNNGKTEY GLFEINNKMW
     CRDNQILPSR NICGISCNKF LDDDLTDDVM CAKKDLDSEG IDYWLAHKPL CSEKLEQWLC
     EEL