Human platelet glycoprotein IX: an adhesive prototype of leucine-rich glycoproteins with flank-center-flank structures.

Abstract

The glycoprotein (GP) Ib-EX complex on the surface of human platelets functions as the von Willebrand factor receptor and mediates von Willebrand factor-dependent platelet adhesion to blood vessels. GPIX is a relatively small (Mr, 17,000) protein that may provide for membrane insertion and orientation of the larger component of the complex, GPIb (Mr, 165,000). Using antibody screening, we cloned a cDNA encoding GPIX from a human erythroleukemia cell cDNA library constructed in phage Agtll. Lacking a 5' untranslated region and start codon, the cDNA sequence includes 604 nucleotides, beinning with 495 bases at the 5' end coding for 165 amino acids, followed by a stop codon and 106 noncoding bases at the 3' end. By Northern blot analysis, the GPIX cDNA hybridizes with a single 1.0-kilobase species ofplatelet poly(A)+ RNA. Translation of the cDNA sequence gives a predicted protein sequence beinning with a truncated putative signal sequence of 5 amino acids followed by a sequence of 17 amino acids matching that determined directly by Edman degradation of intact GPIX. The predicted amino acid sequence of mature GPIX includes an NH2-terminal extracytoplasmic domain of 134 residues, a transmembrane domain of 20 residues, 6 intracytoplasmic residues, and 1 N-linked glycosylation site. GPIX contains a leucine-rich glycoprotein (LRG) sequence of 24 amino acids similar to conserved LRG sequences in GPIb and other proteins from humans, Drosophia, and yeast."Flanking" sequences of %22 amino acids are present at the NH2 and/or COOH sides of the "central" LRG sequence(s) in GPIX, GPIb, and the other human and Drosophila members of the LRG family. The role of the flank-LRG center-flank structure in the evolution and function of the LRG proteins remains to be defined.

Dominant and recessive mutations define functional domains of Toll, a transmembrane protein required for dorsal-ventral polarity in the Drosophila embryo.

“…Injections of lower concentrations (13 t~g/ml) of T1 l°b and T1 ~ transcripts produced more weakly ventralized embryos that resembled those produced by T11 females, with ventral denticle bands encircling the circumference of the larval cuticle. Thus, although TI~°b/+ females produce more strongly ventralized embryos than T1U+ females, the products of both T1 l°b and T1 ~ caused an (Lopez et al 1987(Lopez et al , 1988, human blood platelet glycoprotein IX (gp IX) (Hickey et al 1989), the protein tyrosine kinase receptor trk b (Klein et al 1989), L-rich glycoprotein (LRG) (Takahashi et al 1985), and the lutropin receptor (LHR} (McFarland et al 1989). Amino acid residues are grouped on the basis of similarities between their physical and chemical properties, which were defined according to Miyata expansion of the ventrally derived mesoderm at high concentrations and at lower concentrations expanded the laterally derived ventral epidermis without detectably expanding the mesoderm.…”

“…This clustering of mutations prompted us to examine the carboxy-terminal flanking sequences of other L-rich repeat-containing proteins more closely. In Toil, both blocks of L-rich repeats are followed by a cysteine-containing motif, which is also found in a subset of proteins that have extracellular Lrich repeats including L-rich glycoprotein {Takahashi et al 1985}, the platelet transmembrane proteins gp lb and 13, gp IX (Lopez et al 1987(Lopez et al , 1988Hickey et al 1989}, and the lutropin-choriogonadotropin receptor (McFarland et al 1989}. We found that the similarity between these motifs extends further than described previously {Hickey et Keith and Gay 1990} and that the motifs contain four, rather than only two, conserved cysteine residues {Fig.…”

“…The 803-amino acid residue extracellular domain, of Toll is composed largely of two blocks of leucine-rich (L-rich) repeats. L-rich repeats of this type have been found in a diverse group of proteins including the transmembrane protein platelet protein glycoprotein (gp) lb ~ and f3, gp IX, and the lutropinchoriogonadotropin receptor (Lopez et al 1987(Lopez et al , 1988Hickey et al 1989;McFarland et al 1989). The Drosophila protein chaoptin, which is composed almost exclusively of L-rich repeats, can mediate homotypic cell adhesion (Krantz and Zipursky 1990), and Toll itself can promote heterotypic cell adhesion (Keith and Gay 1990), providing evidence that this motif defines a protein-protein interaction domain.…”

Bernard‐Soulier syndrome Karlstad: Trp 498→Stop mutation resulting in a truncated glycoprotein Ibα that contains part of the transmembranous domain

“…The 145 kD GPIba contains von Willebrand factor (VWF) and thrombin binding sites and is linked to the 27 kD GPIbb by a disulphide bond. The 22 kD GPIX is noncovalently bound and GPV is more weakly associated (Lopez et al, 1987(Lopez et al, , 1988Hickey et al, 1989;Modderman et al, 1992).…”

G→A transition at nucleotide 2110 in the human platelet glycoprotein (GP) IX gene resulting in ALA139(ACC)→THR(GCC) substitution

“…Both Ala and Thr have aliphatic side chains, but the hydroxyl group of Thr side chain makes it more hydrophilic. Since Ala resides within a transmembrane domain of the GPIX polypeptide (Hickey et al, 1989), Ala139~Thr substitution may result in an insufficient surface expression of the GPIb/IX complex. Four individuals homozygous for A/A were analyzed their surface expression of the GPIb/IX complex by a fluorescence-activated cell sorter (FACS).…”