Two identical hydrophobic clusters are present on the same actin monomer: interaction between one myosin subfragment‐1 and two actin monomers

Abstract

Two-dimensional hydrophobic clusters analysis (IICA) was used to compare the distribution of hydrophobic clusters along various actin sequence. HCA-deduced patterns were not altered by amino-acid variations throughout the evolution of actin and we observed similar hydrophobic motifs comprising myosin subfragment-I ATP-independent binding sites. HCA suggested the presence of two groups of identical hydrophobic motifs (A~ and A2) which bound on each side of the S1 (63 kDa-31 kDa) connecting segment in relation with two actin monomers. This connection is important in communications between actin-and nucleotide-binding sites. We postulate that some relation and message between the two motifs A~ and A 2 take place through myosin subfragment-I (63 kDa-31 kDa) connecting segment.1~ ey words'," Acto-myosin; Hydrophobic cluster; Structure comparison 1~ IntroductionIdentification of the actin-myosin interface is essential in t nderstanding the cyclical enzymatic and mechanical process c f myofibrillar contraction.Atomic resolution of the actin structure [1,2] and the threeciimensional atomic model of F-actin decorated with rabbit ~aymotryptic-S1 [3] or Dictyostelium myosin S1 [4] revealed I ~cations of the myosin head on F-actin. This molecular model f the actin-myosin complex derived from the X-ray structure l zveals a close contact between a myosin subfragment-I and 1 ~o actin monomers. A first contact includes carboxyl residues ,2, 3, 4, 24, 25, 99 and 100. In a second contact, exposed actin 1 ydrophobic residues 144, 341,345,349 and 352 are concerned. "he third contact involves proline residues (332-333) of actin. ~11 of these contacts involve a single monomer. A second mon-~,mer is close to the myosin heavy chain and the interaction i ~cludes the cz-helix formed by actin residues Trp79 to Asn92 flat formed a weak binding contact and was cross-linked [5,6].The Taylor-Amos model [7] of acto-S1 suggests that S1 has n extensive contact with an actin monomer (acl) and a weaker ,. ontact with an adjacent actin monomer (ac2); and two differ-,, nt rigor complexes were suggested [8,9], with SI binding to :-actin occurring in two steps with actin monomers. Using .,uccessively EDC and DMS, we previously cross-linked two lnonomers to 20-kDa and 50-kDa skeletal S1 fragments, re-: Corresponding author. Fax: (33) (67) 60 94 78.spectively [10], and in vitro studies showed that subfragment-I alone can produce the sliding movement of the actin filament [111.Chemical cross-linking [12], NMR [13,14] and immunochemical studies [15,16,[17][18][19][20] have pinpointed actin segments in subdomain-1, residues 1 28, 96-103, 112-125, 338 348 and 360-372 which are able to bind with the myosin head.Furthermore, the (27 kDa-50 kDa-20 kDa) trypsin split myosin subfragment-1, which could no longer be activated by actin, did not bind to the two sites located in the 96-125 region, but it still interacted with the 338-348 and 360--372 segments [191. The presence of hydrophobic interactions in the actin myosin complex have already been sugge...

Close Proximity of Myosin Loop 3 to Troponin Determined by Triangulation of Resonance Energy Transfer Distance Measurements

“…Possible Inhibitory Effects of Tn on Actomyosin Interactions. It has been shown before that each myosin head interacts with two actin monomers forming primary and secondary binding sites (14,18,24). Binding of myosin to actin is believed to first involve the formation of a weak ionic interaction and then a stronger stereospecific interaction.…”

“…Various atomic models have been proposed for the relationship between actin and skeletal myosin, but in these models the Tn and Tm complex has not been included − . One problem is that the X-ray crystallographic structures upon which these models are based may not represent the true actin-bound conformation form due to the conditions required to prepare protein crystals.…”