Cap Z, a calcium insensitive capping protein in resting and activated platelets.
Capping of the barbed-ends of actin filaments is an important mechanism for control of the cytoskeleton. In platelets, a valuable model system, it has been thought that gelsolin was the major capping protein. We now report that platelets contain approximately 2 microM Cap Z, a calcium insensitive heterodimeric capping protein; two major and additional minor isoforms of both alpha and beta subunits are present. In lysates from resting platelets 75-80% of the Cap Z sediments with the high speed pellet, but if the platelets are activated with thrombin for 10 s, about 15% of the Cap Z leaves the pellet fraction and is found in the high speed supernatant where it is not bound to actin. This translocation of Cap Z to the supernatant is also observed when resting platelets are lysed into buffer containing 50-100 microM GTP gamma S and 10 mM EGTA. Our results suggest that release of Cap Z from some actin filaments could generate free filament barbed-ends. An increase in free barbed-ends has been reported in platelet lysates prepared shortly after thrombin activation.
Nachmias
V T
VT
Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia 19104-6058, USA.
Golla
R
R
Casella
J F
JF
Barron-Casella
E
E
D000199:Actins / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000737:chemistry* / Q000502:physiology; D051347:CapZ Actin Capping Protein; D005591:Chemical Fractionation; D002645:Chickens; D003599:Cytoskeleton / Q000378:metabolism; D004586:Electrophoresis / Q000379:methods; D019084:Fluorescent Antibody Technique, Indirect; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D008840:Microfilament Proteins; D009124:Muscle Proteins / Q000032:analysis* / Q000737:chemistry / Q000502:physiology*; D015539:Platelet Activation; D011993:Recombinant Fusion Proteins / Q000276:immunology; D013917:Thrombin / Q000378:metabolism / Q000494:pharmacology
D000199:Actins; D051347:CapZ Actin Capping Protein; D008840:Microfilament Proteins; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013917:Thrombin