Structure-activity relationship in vinculin: an IR/attenuated total reflection spectroscopic and film balance study

Interaction of cytoskeletal proteins with membrane lipids

Rapid and significant progress has been made in understanding lipid/protein interactions involving cytoskeletal components and the plasma membrane. Covalent and noncovalent lipid modifications of cytoskeletal proteins mediate their interaction with lipid bilayers. The application of biophysical techniques such as differential scanning colorimetry, neutron reflection, electron spin resonance, CD spectroscopy, nuclear magnetic resonance, and hydrophobic photolabeling, allow various folding stages of proteins during electrostatic adsorption and hydrophobic insertion into lipid bilayers to be analyzed. Reconstitution of proteins into planar lipid films and liposomes help to understand the architecture of biological interfaces. During signaling events at plasma membrane interfaces, lipids are important for the regulation of catalytic protein functions. Protein/lipid interactions occur selectively and with a high degree of specificity and thus have to be considered as physiologically relevant processes with gaining impact on cell functions.

Interaction of the 47-kDa talin fragment and the 32-kDa vinculin fragment with acidic phospholipids: a computer analysis

In recent in vitro experiments, it has been demonstrated that the 47-kDa fragment of the talin molecule and the 32-kDa fragment of the vinculin molecule interact with acidic phospholipids. By using a computer analysis method, we determined the hydrophobic and amphipathic stretches of these fragments and, by applying a purpose-written matrix method, we ascertained the molecular amphipathic structure of alpha-helices. Calculations for the 47-kDa mouse talin fragment (residues 1-433; NH2-terminal region) suggest specific interactions of residues 21-39, 287-342, and 385-406 with acidic phospholipids and a general lipid-binding domain for mouse talin (primary amino acid sequence 385-401) and for Dictyostelium talin (primary amino acid sequence 348-364). Calculations for the 32-kDa chicken embryo vinculin fragment (residues 858-1066; COOH-terminal region) and from nematode vinculin alignment indicate for chicken embryo vinculin residues 935-978 and 1020-1040 interactions with acidic phospholipids. Experimental confirmation has been given for vinculin (residues 916-970), and future detailed experimental analyses are now needed to support the remaining computational data.

Interfacial adsorption and aggregation associated changes in secondary structure of human calcitonin monitored by ATR-FTIR spectroscopy

The peptide hormone human calcitonin (hCT) has a marked tendency to aggregate in aqueous solutions, resulting in viscous and turbid dispersions consisting of long fibrils approximately 80 A in diameter. Both transmission (T-FTIR) and attenuated total reflection Fourier transform infrared (ATR-FTIR) experiments were applied on hCT adsorption and aggregation kinetics. By means of the surface sensitive ATR-FTIR spectroscopy at a hydrophobic/hydrophilic interface, early adsorption and aggregation steps of hCT could be followed in situ under real time conditions. Since the aggregation of hCT is associated with conformational changes, the secondary structure sensitive amide I'-band (D2O) could be used as a diagnostic marker. ATR-FTIR spectra recorded during the aggregation kinetics of hCT showed an increase of the amide I'-band intensity by a factor of 3.4, interpreted as pronounced adsorption of hCT molecules from bulk solution to the germanium plate. Furthermore, variations in the line shape of the amide I'-band were interpreted. At the beginning, hCT adopted a random coil conformation followed by distinct formations of alpha-helical and intermolecular parallel beta-sheet structures. Finally, the random coil content declined to 63%, whereas alpha and beta contents rose to 8% and 29%, respectively. From our kinetics results the alpha-structures were formed faster than the beta-structures. This was interpreted as an initial induction of amphiphilic helices during the adsorption process of hCT monomers. ATR-FTIR spectroscopy provides a sensitive analytical tool suggested to monitor interfacial adsorption and aggregation phenomena also of other peptides and proteins.

Pattern formation and handedness in the cytoskeleton of human platelets

The cytoskeletal patterns of human platelets spread on a glass surface are analyzed. F-actin is arranged in patterns of parallel microfilaments, microfilaments forming triangles, or microfilaments radiating tangentially from a central ellipse or circle. Vinculin, a cytoskeletal protein, is located at both ends of the filaments. In platelets with tangentially radiating microfilaments, vinculin patches are aligned on the branches of a two-armed spiral. The spirals are always left-handed. Talin and two integrins (gpIIb-IIIa, vitronectin receptor), proteins usually associated with focal contacts in tissue culture cells, are not concentrated at the ends of microfilaments in human platelets. It is suggested that the distribution of vinculin is due to competitive aggregation of vinculin close to the inner leaflet of the ventral plasma membrane and that sites of cytoskeleton-membrane linkage are important for generating supramolecular asymmetries of biological systems.

Vinculin

Vinculin is clearly a key element in the transmembrane assemblages that link cells to each other or to the substrate. However, despite all the studies that have been done on the protein, we still do not know its function within these assemblages. The bulk of the biochemical and cell biological evidence suggests that, in some unknown way, its presence in the junctions may be involved in the stable association of actin with the membrane, yet vinculin by itself does not appear to interact with actin. In the future, identification of additional junctional molecules that interconnect actin and vinculin may resolve this dilemma. Alternatively, studies with vinculin that is phosphorylated or acylated may yield clues to its function. Perhaps the complexity of the protein composition of microfilament-containing junctions suggests that protein assemblages rather than individual proteins provide novel functions. As new proteins belonging to these junctions are discovered, it will be important to assess their interaction with already known components such as vinculin and to ask if the protein combination has a particular function.

The cytoskeletal protein vinculin contains transformation-sensitive, covalently bound lipid

Vinculin, which is associated with the cytoskeleton of many cells, has been suggested as a possible linker between microfilament bundles and the plasma membrane. Here it will be shown that fatty acid is covalently attached to vinculin in vivo. Furthermore, in chicken embryo fibroblasts infected with a temperature-sensitive mutant of Rous sarcoma virus, tsNY68, the acylation of vinculin at the permissive temperature was less than one-third that at the nonpermissive temperature. Thus, the covalent binding of lipid to vinculin is a transformation-sensitive event. The covalent modification of vinculin by lipids could be directly or indirectly involved in its reversible association with membranes. This modification may also provide a mechanism to alter the organization of vinculin within cells and thereby play a regulatory role in anchoring or stabilizing microfilament bundles at plasma membranes.