Polycation induced actin bundles

Abstract

Three polycations, polylysine, the polyamine spermine and the polycationic protein lysozyme were used to study the formation, structure, ionic strength sensitivity and dissociation of polycation-induced actin bundles. Bundles form fast, simultaneously with the polymerization of MgATP-G-actins, upon addition of polycations to solutions of actins at low ionic strength conditions. This indicates that nuclei and/or nascent filaments bundle due to attractive, electrostatic effect of polycations and the neutralization of repulsive interactions of negative charges on actin. The attractive forces between the filaments are strong, as shown by the low (in nanomolar range) critical concentration of their bundling at low ionic strength. These bundles are sensitive to ionic strength and disassemble partially in 100mM NaCl, but both the dissociation and ionic strength sensitivity can be countered by higher polycation concentrations. Cys374 residues of actin monomers residing on neighboring filaments in the bundles can be cross-linked by the short span (5.4 Å) MTS-1 (1,1-Methanedyl Bismethanethiosulfonate) cross-linker, which indicates a tight packing of filaments in the bundles. The interfilament cross-links, which connect monomers located on oppositely oriented filaments, prevent disassembly of bundles at high ionic strength. Cofilin and the polysaccharide polyanion heparin disassemble lysozyme induced actin bundles more effectively than the polylysine-induced bundles. The actin-lysozyme bundles are pathologically significant as both proteins are found in the pulmonary airways of cystic fibrosis patients. Their bundles contribute to the formation of viscous mucus, which is the main cause of breathing difficulties and eventual death in this disorder.

Polyelectrolyte properties of filamentous biopolymers and their consequences in biological fluids

“…Data for F-actin taken from 30, 49 , for CSA13 from 67 , LL37 from 94, 99 , vimentin from 82, 114 , Pf1 from 12 , fd from 115 , Lys18 from 30 , F-actin/spermine from 14 , DNA and spermine from 116 , DNA and cobalt hexamine from 117 .…”

Actin bundling and polymerisation properties of eukaryotic elongation factor 1 alpha (eEF1A), histone H2A–H2B and lysozyme in vitro

“…It must be noted that in some instances some actin bundling appeared when eEF1A was not present. This is not unusual, as there is a large body of literature showing that, due to the polyelectrolyte nature of F-actin, bundles can form without the presence of specific actin binding proteins (Tang et al, 1997(Tang et al, , 2001Xian et al, 1999;Angelini et al, 2003;Muhlrad et al, 2011). However, these bundles differed from those which were formed due to the presence of eEF1A in that there were less of them and they were somewhat smaller in diameter Interestingly, we found that, when phalloidin was not present but eEF1A was AFM images still revealed the presence of intact F-actin filaments exhibiting bundling, thus indicating that eEF1A has some stabilising affect on F-actin.…”

Uncovering protein polyamination by the spermine-specific antiserum and mass spectrometric analysis

“…Cationic molecules including polyamines induce actin bundles (Muhlrad et al 2011) and specific growth of actin-enriched lamellipodia in cells (Nedeva et al 2013) and promote the bundling of microtubules (Hamon et al 2011). In addition, transglutaminase-catalyzed polyamination of tubulins stabilizes microtubules in vitro and in vivo (Song et al 2013).…”