ID   A2M_HOMAM               Reviewed;          38 AA.
AC   P20737;
DT   01-FEB-1991, integrated into UniProtKB/Swiss-Prot.
DT   01-FEB-1991, sequence version 1.
DT   25-MAY-2022, entry version 70.
DE   RecName: Full=Alpha-2-macroglobulin homolog;
DE            Short=Alpha-2-M;
DE   Flags: Fragments;
OS   Homarus americanus (American lobster).
OC   Eukaryota; Metazoa; Ecdysozoa; Arthropoda; Crustacea; Multicrustacea;
OC   Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Astacidea;
OC   Nephropoidea; Nephropidae; Homarus.
OX   NCBI_TaxID=6706;
RN   [1]
RP   PROTEIN SEQUENCE.
RC   TISSUE=Hemolymph;
RX   PubMed=2444589; DOI=10.1016/s0021-9258(18)47839-8;
RA   Spycher S.E., Arya S., Isenman D.E., Painter R.H.;
RT   "A functional, thioester-containing alpha 2-macroglobulin homologue
RT   isolated from the hemolymph of the American lobster (Homarus americanus).";
RL   J. Biol. Chem. 262:14606-14611(1987).
CC   -!- FUNCTION: Is able to inhibit all four classes of proteinases by a
CC       unique 'trapping' mechanism. This protein has a peptide stretch, called
CC       the 'bait region' which contains specific cleavage sites for different
CC       proteinases. When a proteinase cleaves the bait region, a
CC       conformational change is induced in the protein which traps the
CC       proteinase. The entrapped enzyme remains active against low molecular
CC       weight substrates (activity against high molecular weight substrates is
CC       greatly reduced). Following cleavage in the bait region a thioester
CC       bond is hydrolyzed and mediates the covalent binding of the protein to
CC       the proteinase.
CC   -!- SUBUNIT: Homodimer; disulfide-linked.
CC   -!- SUBCELLULAR LOCATION: Secreted.
CC   -!- TISSUE SPECIFICITY: Hemolymph.
CC   -!- SIMILARITY: Belongs to the protease inhibitor I39 (alpha-2-
CC       macroglobulin) family. {ECO:0000305}.
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DR   PIR; A29481; A29481.
DR   AlphaFoldDB; P20737; -.
DR   MEROPS; I39.007; -.
DR   GO; GO:0005615; C:extracellular space; IEA:InterPro.
DR   GO; GO:0004867; F:serine-type endopeptidase inhibitor activity; IEA:UniProtKB-KW.
DR   InterPro; IPR011626; Alpha-macroglobulin_TED.
DR   InterPro; IPR019742; MacrogloblnA2_CS.
DR   Pfam; PF07678; TED_complement; 1.
DR   PROSITE; PS00477; ALPHA_2_MACROGLOBULIN; 1.
PE   1: Evidence at protein level;
KW   Bait region; Direct protein sequencing; Disulfide bond; Protease inhibitor;
KW   Secreted; Serine protease inhibitor; Thioester bond.
FT   CHAIN           1..>38
FT                   /note="Alpha-2-macroglobulin homolog"
FT                   /id="PRO_0000093791"
FT   CROSSLNK        27..30
FT                   /note="Isoglutamyl cysteine thioester (Cys-Gln)"
FT   NON_CONS        22..23
FT                   /evidence="ECO:0000305"
FT   NON_TER         38
SQ   SEQUENCE   38 AA;  4251 MW;  865F8E00E212CF32 CRC64;
     SYIITTPRMW VAGSPAQVRT YVMPYGCGEQ NMVNFAPN