Small Integrin Binding LIgand N-linked Glycoproteins
Family members include:
bone sialoprotein (BSP), osteopontin (OPN), dentin matrix protein-1 (DMP-1), dentin
secreted phosphoprotein (DSPP), and matrix extracellular phosphoglycoprotein (MEPE)
Is this a real family?
Evidence against:
no strong homologies at the amino acid level
overall chemical properties are different
BSP, DMP1, DSPP and OPN are all acidic while MEPE is strongly basic
Within acidic members, BSP is glutamic acid-rich, OPN is aspartic acid-rich, while DMP1 is a mix of the two
Evidence for:
clustering of genes within a single chromosome
similarity of their intron-exon boundaries
biochemical similarities of their corresponding exons
Exon 1 is always a noncoding exon.
Exon 2 always contains the start codon, the leader
sequence and the codons for the first two amino acids of the mature
proteins.
Exon 3 usually contains a casein kinase II phosphorylation site (SSEE.
Exon 4 is usually relatively proline-rich (PPPP).
Exon 5 usually contains another casein kinase II phosphorylation site
The last one or two exons encode the vast majority of the
protein and always contain the integrin-binding tripeptide, RGD
