High impact information on MYO2

• Actin, myosin 2, and clathrin heavy chain are involved in mating partner discrimination, since strains carrying mutations in the genes encoding these proteins result in a small but significant defect in mating partner discrimination [1].
• These serve as tracks for the transport of secretory vesicles, the segregation of the trans Golgi network, the vacuole, peroxisomes, endoplasmic reticulum, mRNAs for cell fate determination, and microtubules that orient the nucleus in preparation for mitosis, all by myosin-Vs encoded by the MYO2 and MYO4 genes [2].
• For example, the yeast class V myosin, Myo2p, moves several organelles to distinct locations during the cell cycle [3].
• Vac17p binds simultaneously to Myo2p and to Vac8p, a vacuolar membrane protein [3].
• The tail domain of Myo2 that binds Kar9 also interacts with secretory vesicles and vacuolar elements, making it a pivotal component of yeast cell polarization [4].

Biological context of MYO2

• Alterations of MYO4 or MYO2 indicate that neither the motor domains nor tails of these myosins are required to confer the overexpression phenotype, whereas the neck region may be required [5].
• However, overexpression of MYO4 or MYO2 results in several morphological abnormalities, including the formation of short strings of unseparated cells in diploid strains, or clusters of cells in haploid strains [5].
• The data support a model in which the Myo2p tail tethers secretory vesicles, and the motor transports them down polarized actin cables to the site of exocytosis [6].
• In contrast, a different point mutation, mlc1-11, displayed defects in cytokinesis and in interactions with Myo2p and Iqg1p [7].
• The tail domain of Myo2p is sufficient for localization at low- expression levels and causes mislocalization of the endogenous Myo2p from sites of polarized cell growth [8].

Anatomical context of MYO2

• MYO2 encodes a type V myosin heavy chain needed for the targeting of vacuoles and secretory vesicles to the growing bud of yeast [6].
• In contrast, retention of mitochondria in the bud was compromised in YPT11 and MYO2 mutants [9].
• We noted a correlation in the behavior of Myo2p, Smy1p, and actin, but not microtubules, under a number of circumstances [10].
• Moreover, the myo2-66 mutant, which carries a temperature-sensitive mutation in the Myo2p motor domain, exhibited a 55% decrease in accumulation of mitochondria in the bud tip, and an increase in accumulation of mitochondria at the retention site in the mother cell after shift to restrictive temperatures [9].
• In Saccharomyces cerevisiae, the class V myosin, Myo2p, is involved in transporting different organelles, including the peroxisome, along actin cables to the bud [11].

Associations of MYO2 with chemical compounds

• The Myo2p in this pellet is not solubilized by Mg++-ATP or Triton X-100, but is solubilized by high salt [8].
• The wild-type MYO2 gene encodes an essential form of myosin composed of an NH2-terminal domain typical of the globular, actin-binding domain of other myosins [12].
• Unexpectedly, we found that abolition of microtubules by nocodazole does not interfere with the ability of Smy1p to correct the mutant Myo2p defect, nor does it interfere with the ability of Smy1p to localize properly [13].
• Myo2p motility is Ca(2+) insensitive [14].
• Third, Myo2p coimmunoprecipitates with calmodulin in the presence of Ca2+ or EGTA [15].

Physical interactions of MYO2

• Gel overlay assay shows that a mutant calmodulin with the F92A alteration has severely reduced binding affinity to a GST-Myo2p fusion protein [16].
• Vac17p interacts with the Myo2p cargo-binding domain, but not with vacuole inheritance-defective myo2 mutants that have single amino acid changes within this region [17].
• This suggests that Myo2p serves as a molecular motor for vacuole transport along actin filaments [18].
• The crystal structures of Mlc1p bound to IQ2 and IQ4 of Myo2p differ dramatically [19].
• We now show by two-hybrid analysis that a 69-amino acid region of the Smy1p tail interacts with the globular portion of the Myo2p tail [20].

Co-localisations of MYO2

• Deletion of this myosin-binding region of Smy1p eliminates its ability to colocalize with Myo2p and to overcome the myo2-66 mutant defects, suggesting that the interaction is necessary for these functions [20].

Regulatory relationships of MYO2

• We propose that Smy1p enhances some aspect of Myo2p function, perhaps delivery or docking of vesicles at the bud tip [20].

Other interactions of MYO2

• We noted that the myo2 mutant can recover from osmotic shift (unlike actin mutants; Novick, P., and D. Botstein. 1985. Cell. 40:405-416) [10].
• However, the lethality of MYO2 deletion is not overcome by SMY1 overexpression [10].
• Reduced levels of MYO2 overcome the haploinsufficiency of MLC1 [21].
• The myo2-66 conditional mutation shows synthetic lethality with the TPM1 disruption, indicating that the MYO2 and TPM1 gene products may be involved in the same, or parallel function [22].
• A comparison with other myosins in GenBank reveals that Myo4 protein is most closely related to the yeast Myo2 protein, another class V myosin [5].

Analytical, diagnostic and therapeutic context of MYO2

• Immunofluorescence localization of the unconventional myosin, Myo2p, and the putative kinesin-related protein, Smy1p, to the same regions of polarized growth in Saccharomyces cerevisiae [10].
• Random replacement and site-directed mutagenesis at position 92 of calmodulin indicate that hydrophobic and aromatic residues are allowed at this position, suggesting an importance of hydrophobic interaction between calmodulin and Myo2p [16].
• First, as assessed by indirect immunofluorescence, the distributions of Myo2p and calmodulin are nearly indistinguishable throughout the cell cycle [15].

References