Steric hindrance in the upper 50 kDa domain of the motor Myo2p leads to cytokinesis defects in fission yeast

Abstract

Cytokinesis in many eukaryotes requires a contractile actomyosin ring that is placed at the division site. In fission yeast, which is an attractive organism for the study of cytokinesis, actomyosin ring assembly and contraction requires the myosin II heavy chain Myo2p. Although myo2-E1, a temperature-sensitive mutant defective in the upper 50 kDa domain of Myo2p, has been studied extensively, the molecular basis of the cytokinesis defect is not understood. Here, we isolate myo2-E1-Sup2, an intragenic suppressor that contains the original mutation in myo2-E1 (G345R) and a second mutation in the upper 50 kDa domain (Y297C). Unlike myo2-E1-Sup1, a previously characterized myo2-E1 suppressor, myo2-E1-Sup2 reverses actomyosin ring contraction defects in vitro and in vivo. Structural analysis of available myosin motor domain conformations suggests that a steric clash in myo2-E1, which is caused by the replacement of a glycine with a bulky arginine, is relieved in myo2-E1-Sup2 by mutation of a tyrosine to a smaller cysteine. Our work provides insight into the function of the upper 50 kDa domain of Myo2p, informs a molecular basis for the cytokinesis defect in myo2-E1, and may be relevant to the understanding of certain cardiomyopathies.

RNA binding of Hfq monomers promotes RelA-mediated hexamerization in a limiting Hfq environment

“…As wild type RelA carries tyrosine, an aromatic amino acid residue at position 290, the mutational change C289Y resulted in two consecutive tyrosine residues that were expected to cause steric hindrance because of their bulky side chains (35). The double mutant RelA:C289Y;Y290C in which the tyrosine residue at position 290 was changed to cysteine was more effective in mediating repression than the single C289Y mutant, suggesting that C289Y causes steric hindrance and that RelA-mediated regulation relies primarily on structural elements ( Figure 1A, Figure S1).…”

The fission yeast cytokinetic ring component Fic1 promotes septum formation

“…myo2-E1 is a temperature-sensitive allele of the essential type-II myosin, myo2 , that inhibits Myo2’s activity and produces non-constricting CRs at the restrictive temperature (Balasubramanian et al, 1998; Palani et al, 2017; Palani et al, 2018). Without CR constriction, cell wall accumulates at the division site but does not form a septum (Balasubramanian et al, 1998; Palani et al, 2017; Palani et al, 2018; Ramos et al, 2019). Interestingly, fic1Δ did not suppress myo2-E1 and no genetic interaction was observed between fic1-2D and myo2-E1 (Fig.…”

The fission yeast cytokinetic ring component Fic1 promotes septum formation

“…myo2-E1 is a temperature-sensitive allele of the essential type-II myosin, myo2 , that inhibits Myo2's activity and produces non-constricting CRs at the restrictive temperature ( Balasubramanian et al, 1998 ; Palani et al, 2017 , 2018 ). Without CR constriction, cell wall accumulates at the division site but does not form a septum ( Balasubramanian et al, 1998 ; Palani et al, 2017 , 2018 ; Ramos et al, 2019 ). Interestingly, fic1 Δ did not suppress myo2-E1 and no genetic interaction was observed between fic1-2D and myo2-E1 ( Fig.…”