Profilin actin complexes

Figure 1. Localization of profilin and/or profilin-actin complex into an activated cluster. VASP, Vasodilator-stimulated phospho-protein.

This cross-axis CPC provides the universal application of protein samples with a dextran-PEG polymer-phase system. Using a prototype of the L cross-axis CPC with a 130-mL column capacity, profilin-actin complex was purified directly from a crude extract otAcanthamoeba with the same solvent system as used for the serum protein separation earlier. The sample solution was prepared by adding proper amounts of PEG 8000 and dex-tran T500 to 2.5 g of the Acanthamoeba crude extract to adjust the two-phase composition similar to that of the solvent system used for the separation. The experiment was performed by eluting the upper phase at 0.5 mL/min under a high revolution rate of 1000 rpm. The profihn-actin complex was eluted between 60 mL and 84 mL fractions and well separated from other compounds. The retention of the stationary phase was 69.0% of the total column capacity. 

Second, as a complex with G-actin, profilin is postulated to assist in the addition of monomers to the (-f) end of an actin filament. This hypothesis is consistent with the three-dimensional structure of the profilin-actin complex in which profilin is bound to the part of an actin monomer opposite the ATP-binding end, thereby leaving it free to associate with the (+) end of a filament (see Figure 19-3). After the complex binds transiently to the filament, the profilin dissociates from actin. 

Finally, profilins have been reported as residents of the nucleus. Immunofluorescence revealed nuclear profilin I in fibroblasts and epithehal cells (Mayboroda et al. 1997 Skare et al. 2003) and in bovine oocyte germinal vesicles and early embryos (Rawe et al. 2006). Nuclear profilin has also been described in several higher plants (see Hussey et al. 2006 for original references). Additionally, the existence of nuclear profilin-actin complexes can be deduced from studies on HeLa cells and Xenopus oocytes (Striven et al. 2003). In a recent study with GFP-profilin transfected cells and polyclonal anti-serum, profilin II has been shown to accumulate in the nucleus of hippocampal neurons. This concentration was de-... 

Multidomain proteins of the above quoted families and profilin participate not only in lamellipodial protmsion during locomotion but also in cell adhesion VASP and profilin are both regular components of nascent adhesion complexes in spreading tissue culture cells (Hiittelmaier et al. 1998 and unpublished observations). In summary, the numerous profilin ligands and their different local concentrations may control actin polymerization, in conjunction with profilin-actin complexes, in a time- and space-controlled manner. Figure 3 presents a hypothetical model with selected examples of such processes at the cell membrane. 

Profilin-actin complex from Acanthamoeba extract. ... 

Fig. 3 Schematic representation of the multiple functional involvement of profilin at the plasma membrane. The ratio between membrane-bound and free profilin is regulated by the level of PIP2 and determines the complex formation of profilin with G-actin. Upon release from the membrane, profilin is involved in charging G-actin with ATP (center). Subsequently, the profilin-ATP-G-actin complex adds to nascent actin filaments and participates in the generation of actin filaments as needed for adhesion complexes Qeft) and lamellipodial actin networks (right). Details of this scenario show only selected examples of all possible constellations and are thus highly speculative, but consistent with the present knowledge...

BASIC FEATURES OF THE ACTIN-BASED MOTOR COMPLEX. These experiments support the following model for Listeria actin-based motility. The Listeria surface protein ActA uses its oligoproline sequences (FEFPPPPTDE) to bind the host cell protein VASP. VASP in turn deploys its own larger set of GPPPPP sequences to bind profilin. 

Machesky LM, Atkinson SJ, Ampc C et al. Purification of a cortical complex containing two unconventional actins from Acanthamoeba by affinity chromatography on profilin-agarose. J Cell Biol 1994 127 107-15. 

Baker HI, Goodman AL, Rodal AA et al. Coordinated regulation of actin filament turnover by a high-molecular-wcighi Srv2/CAP complex, cofilin, profilin and Aipl. Curr Biol 2003 ... 

Promotion of Actin Assembly by Profilin Another cytosolic protein, profilin (15,000 MW), also binds ATP-actin monomers in a stable 1 1 complex. At most, profilin can buffer 20 percent of the unpolymerized actin in cells, a level too low for it to act as an effective sequestering protein. Rather than sequestering actin monomers, the main function of profilin probably is to promote the assembly of actin filaments in cells. It appears to do so by several mechanisms. 

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