multimerin-1; emilin-4; elastin microfibril interface located protein 4; elastin microfibril interfacer 4; endothelial cell multimerin; contains: platelet glycoprotein Ia*; contains: 155 kD platelet multimerin; p-155; p155 (MMRN1, ECM, EMILIN4, GPIA* MMRN)
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Function
- carrier protein for platelet factor V/Va*
- storage & stabilization of factor V in platelets
- upon release following platelet activation, may limit platelet & plasma factor Va-dependent thrombin generation
- ligand for integrin alpha-IIb/beta-3 & integrin alpha-V/beta-3 on activated platelets, & may function as an extracellular matrix or adhesive protein
- interacts with factor V/factor Va
Structure
- the N-terminus is blocked
- extensively N-glycosylated
- multimeric
- composed of varying sized, disulfide-linked multimers; the smallest is a homotrimer
- proteolysis of the promultimerin in the N-terminal region, leads to the mature p155 form that is stored in platelets
- contains 1 C1q domain
- contains 1 EGF-like domain
- contains 1 EMI domain
Compartment
Alternative splicing
named isoforms=2
Expression
- synthesized by endothelial cells & megakaryocytes
- stored in platelet alpha granules & endothelial cell Weibel-Palade bodies, following activation of these cells
- released & attached to megakaryocytes, platelets, endothelium & subendothelium of blood vessels
- not found in plasma
- found in vascular tissues such as placenta, lung, & liver
Pathology
- deficiency in multimerin 1 due to proteolytic degradation within the platelet alpha granules is associated with factor V Quebec