Comparison of the binding character of triflavin on resting and activated alpha(IIb)beta(3) integrin in human platelets by electron microscopy.
Triflavin, an Arg-Gly-Asp (RGD)-containing disintegrin purified from venom peptide inhibited platelet aggregation by interfering with the interaction of fibrinogen with alpha(IIb)beta(3) integrin. Using an immunostaining technique and electron microscopy, we investigated and compared the distribution of triflavin binding in both resting and activated platelets. Triflavin uniformly and strongly stained the plasma membrane and the open canalicular system (OCS), whereas a lesser extent of staining was seen on alpha-granules in both resting and activated platelets. Furthermore, resting unfixed platelets were incubated with triflavin for 10 min at 4 degrees C, and then rewarmed at 30 degrees C for 0, 10, and 30 min to advance internalization. At 0 min, platelets showed an extensive rim-staining pattern of bound triflavin on the surface membrane, which was then gradually internalized into the cytoplasmic OCS with prolonging of incubation times. However, triflavin bound fewer to alpha-granules than to the OCS within the 0-30-min period of internalization in both resting and activated platelets. Furthermore, triflavin did not influence physiological endocytosis in resting platelets. Comparing the 3D structures of triflavin and another disintegrin, echistatin, we found that the spatial differences between the RGD motif and the C-termini of structures of disintegrins may mediate functional differences of binding activity towards alpha(IIb)beta(3) integrin in resting platelets. These data indicate that (1) triflavin binds effectively to alpha(IIb)beta(3) on the platelet membrane and cytoplasmic OCS, but a relative lesser extent to alpha-granules in both resting and activated platelets; (2) triflavin is internalized in resting platelets independent of cellular activation; and (3) spatial differences between the RGD motif and the C-termini of disintegrins may play an important role in mediating disintegrin binding to alpha(IIb)beta(3) in resting platelets.
Chuang
Woei-Jer
WJ
Department of Biochemistry, National Cheng Kung University, Medical College, Tainan, Taiwan.
Wu
Ching-Hsiang
CH
Huang
He-Nan
HN
Chen
Seu-Hwa
SH
Hsiao
George
G
Lin
Chien-Huang
CH
Sheu
Joen-Rong
JR
D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000648:ultrastructure; D004705:Endocytosis / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D008854:Microscopy, Electron; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000493:pharmacokinetics* / Q000494:pharmacology; D010975:Platelet Aggregation Inhibitors / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D013329:Structure-Activity Relationship
D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C057986:echistatin; C070025:triflavin