ISSN:
1432-1017
Keywords:
GPIIb, GPIIIa, and GPIIb/IIIa heterodimer
;
Platelet fibrinogen receptor
;
Molecular mass, size, shape and self-association
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Physics
Notes:
Abstract Human platelet plasma membrane glycoproteins IIb (GPIIb) and IIIa (GPIIIa) form a Ca2+-dependent heterodimer, the integrin GPIIb/IIIa, which serves as the receptor for fibrinogen and other adhesive proteins at the surface of activated platelets. Below the critical micellar concentration of Triton X100 (TtX), the three glycoproteins do not bind appreciably to TtX and form association products of large size. The size-exclusion chromatographic patterns of GPIIb, GPIIIa and GPIIb/IIIa have been obtained at 0.2% TtX, and the molecular properties of the association products and monomer fractions have been determined by analysis of the detergent bound to the glycoproteins, laser-light scattering, sedimentation velocity, and electron microscopy (TEM). The monomer of the GPIIb-TtX complex was identified by the molecular mass (M) of the glycoprotein moiety (125 ± 15 kDa), the molecular size (9.5 ± 1.5 nm × 11 ±1.5 nm) and globular shape observed by TEM. It has a molecular mass (M *) of 197 ± 20 kDa, a sedimentation coefficient inf20 supo* of 5.8±0.1 S, a Stokes radius R infs sup* of 6.8±0.4 nm, and a frictional ratio f */ infmin sup* of 1.7±0.14. The (GPIIb) n -TtX complexes are disulphide-bonded size-heterogeneous association products of GPIIb, tetramers being the smallest species found. GPIIIa has a greater propensity to self-associate than GPIIb, this tendency being lower below 1 mg GPIIIa/ml, 0.1 mM Ca2+, pH 9.0. The (GPIIIa) n -TtX complexes are noncovalent size-heterogeneous association products of GPIIIa, tetramers being the smallest form observed. The monomer of the GPIIIa-TtX complex was identified by the 103 ±15 kDa M determined for the glycoprotein moiety, and the 9 ± 1.5 nm × 10 ± 1.5 nm size and globular shape observed by TEM. It has a M * of 136 ± 15 kDa, a s inf20 supo* of 3.9 ± 0.3 S, a R infs /p* of 6.4 ± 0.5 nm, a f */f infmin sup* of 1.9 ± 0.3, and, when stored at pH 7.4, has a certain tendency to form filamentous association products (20–70 nm × 2–5 nm), as observed by TEM. The GPIIb/IIIa-TtX complex in 0.2% TtX/0.1 mM Ca2+ elutes as a single monomeric fraction, as deduced from the 210 ± 15 kDa M determined for its glycoprotein moiety and the 12 ± 1.5 nm × 14 ± 1.5 nm size of the globular forms observed by TEM. The GPIIb/IIIa-TtX complex has a M * of 315±20kDa, a s inf20 sup* of 8.9±0.2 S, a infs sup* of 7.4±0.2 nm, a f */f infmin sup* of 1.5±0.12, and appears in the electron micrographs in multiple forms (filled globular, empty oval, head-two-tails, and bilobular shapes), which on lowering the TtX concentration tend to self-associate, forming a bundant rosettes below the TtX critical micellar concentration.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00183324
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