摘要:

AbstractProfilactin, the profiling:actin complex, which is present in large amounts in extracts of many types of eukaryotic cells, appears to serve as the precursor of microfilaments. It was reported recently that profilactin interacts specifically with phosphatidylinositol 4,5‐bisphosphate (PtdIns(4,5)P2) (Lassing and Lindberg:Nature314:472–474, 1985.) The present paper describes in detail the behaviour of profilactin and profilin in the presence of different types of phospholipids and neutral lipids under different conditions. PtdIns(4,5)P2is the only phospholipid found so far which in the presence of 80 mM KC1 and at Ca2+concentrations below 10−5M effectively dissociates profilactin with the resulting polymerization of the actin. Phosphatidylinositol 4‐monophosphate exhibits some activity but phosphatidylinositol is inactive. Both calf spleen profilin and profilin from human platelets form stable complexes with PtdIns(4,5)P2micelles. PtdIns(4,5)P2is active also when incorporated together with other phospholipids in mixed v

ISSN:0730-2312    

DOI:10.1002/jcb.240370302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractAnalogues of the human erythroid membrane skeletal component protein 4.1 have been identified in perfused rat tissues and human T and B lymphocyte cell lines, olyclonal antibodies were used which are specific for all domains of protein 4.1, the spectrin‐actin‐promoting 8‐Kd peptide, the membrane‐binding 30‐Kd domain, and the 50‐Kd domain. Antibody reactivity, by Western blotting of tissue homogenates, shows reactivity with proteins varying in molecular weight from 175 Kd to 30 Kd. Further, these protein 4.1 analogues appear to be expressed in a tissue‐specific fashion. Of the analogues detected there appear to be at least three classes: analogues containing all erythroid protein 4.1 domains, analogues containing all domains but with modified antigenic epitopes, and analogues containing only some domains. Chemical cleavage at cysteine linkages indicates that in analogues containing the 30‐Kd region the location of cysteine is highly conserved. This datum suggests that in nonerythroid 4.1 isoforms of higher molecular weight the additional protein mass is added to the amino terminal

ISSN:0730-2312    

DOI:10.1002/jcb.240370303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractAggregation‐competent amoeboid cells ofDictyostelium discoideumare chemotactic toward cAMP. Video microscopy and scanning electron microscopy were used to quantitate changes in cell morphology and locomotion during uniform upshifts in the concentration of cAMP. These studies demonstrate that morphological and motile responses to cAMP are sufficiently synchronous within a cell population to allow relevant biochemical analyses to be performed on large numbers of cells.Changes in cell behavior were correlated with F‐actin content by using an NBD‐phallacidin binding assay. These studies demonstrate that actin polymerization occurs in two stages in response to stimulation of cells with extracellular cAMP and involves the addition of monomers to the cytochalasin D‐sensitive (barbed) ends of actin filaments. The second stage of actin assembly, which peaks at 60 sec following an upshift in cAMP concentration, is temporally correlated with the growth of new pseudopods. The F‐actin assembled by 60 sec is localized in these new pseudopods.These results indicate that actin polymerization may constitute one of the driving forces for pseudopod extension in amoeboid cells and that nucleation sites regulating polymerization are under the control of chemotaxis

ISSN:0730-2312    

DOI:10.1002/jcb.240370304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractAnkyrin mediates the primary attachment between beta spectrin and protein 3. Ankyrin and spectrin interact in a positively cooperative fashion such that ankyrin binding increases the extent of spectrin tetramer and oligomer formation (Giorgi and Morrow: submitted, 1988). This cooperative interaction is enhanced by the cytoplasmic domain of protein 3, which is prepared as a 45–4l‐kDa fragment generated by chymotryptic digestion of erythrocyte membranes. Using sensitive isotope‐ratio methods and non‐denaturing PAGE, we now demonstrate directly (1) the enhanced affinity of ankyrin for spectrin oligomers compared to spectrin dimers; (2) a selective stimulation of the affinity of ankyrin for spectrin oligomer by the 43‐kDa cytoplasmic domain of protein 3; and (3) a selective reduction in the affinity of ankyrin for spectrin tetramer and oligomer after its phosphorylation by the erythrocyte cAMP‐independent membrane kinase. The phosphorylation of ankyrin does not affect its binding to spectrin dimer. Ankyrin also enhances the rate of interconversion between dimer‐tetramer‐oligomer by 2–3‐fold at 30°C, and in the presence of the 43‐kDa fragment, ankyrin stimulates the rate of oligomer interconversions by nearly 40‐fold at this temperature. These results demonstrate a long‐range cooperative interaction between an integral membrane protein and the peripheral cytoskeleton and indicate that this linkage may be regulated by covalent protein phosphorylation. Such interactions may be of general import

ISSN:0730-2312    

DOI:10.1002/jcb.240370305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractCaldesmon was originally purified from gizzard smooth muscle as a major calmo‐dulin‐binding protein which also interacts with actin filaments. It has an alternative binding ability to either calmodulin or actin filaments depending upon the concentration of Ca2+(“flip‐flop binding”). Two forms of caldesmon (Mr's in the range of 120–150 kDa and 70–80 kDa) have been demonstrated in a wide variety of smooth muscles and nonmuscle cells. Immunohistochemical studies suggest that caldesmon is colocalized with actin filaments in vivo. Considering its abundance, the Ca2+‐dependent flip‐flop binding ability to either calmodulin or actin filaments, and its intracellular localization, caldesmon is expected to be involved in contractile events. Recent results from our laboratory have led to the conclusion that caldesmon regulates the smooth muscle and nonmuscle actin‐myosin interaction and the smooth muscle actin‐high Mr actin‐binding protein (ABP or filamin) interactin in a flip‐flop manner. It might function in cell motility by regulati

ISSN:0730-2312    

DOI:10.1002/jcb.240370306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractReticuloendotheliosis virus strain T (REV‐T)‐transformed cells gave rise spontaneously to variants which secrete a factor that forms a distinct visible ring of precipitation (halo) surrounding colonies grown in soft agar. An Mr15,000 protein was produced at higher levels by halo variants than by nonhalo‐producing cells. An assay designed to detect the formation of precipitates enabled purification of an Mr15,000 protein, p15, from serum‐free medium conditioned by the growth of REV‐T‐trans‐formed hematopoietic cells. Fractions enriched in p15 permitted the growth of REV‐T‐ trans formed cells under conditions where they normally fail

ISSN:0730-2312    

DOI:10.1002/jcb.240370307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240370301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY