Phenamacril: a potent, but reversible, inhibitor of Fusarium class I myosin

Fungicide application remains a vital component in the management of Fusarium-induced plant infections, but environmental concerns and resistance toward some of the commonly used fungicides has spurred efforts into developing new specific fungicides. Phenamacril, a cyanoacrylate fungicide, represents a novel class of seemingly Fusarium-specific and environmentally benign fungicides that could hold great potential in our future efforts toward minimizing the occurrence and severity of Fusarium-induced plant infections. Phenamacril targets the motor domain of Fusarium class I myosin [1-2], an ubiquitous molecular motor which facilitates numerous ATP-driven and actin-associated processes within the cell. The myosin superfamiliy is divided into approximately 20 different classes (classes I, II, V and XVII are present in fungi), each potentially having several isoforms. While the taskspecific C-terminal tail domains are highly variable in size and function, the N-terminal motor domains remain highly conservered, both structurally and functionally. Interestingly, Phenamacril-resistance has been shown to correlate with single amino acid mutations in a highly conserved region of the motor domain [1], a region involved in the allosteric communication between the actin- and nucleotide binding-site [3]. To gain further insight into the specificity, the inhibitory potential and nature of the Phenamacril-mediated inhibitionof Fusarium myosin, we overexpressed Fusarium class I myosins in Sf9 insect cells. Through a combination of NADH-coupled and in vitro motility assays, we demonstrated that Phenamacril is a very potent but functionally reversible inhibitor of Fusarium class I myosin. Similarly, we demonstrated that Phenamacril had no or only minimal inhibitory effect on human myosin 1c, Dictyostelium discoideum class I and II myosins, but that the motor domain of the Phenamacril-resistant F. solani f. sp. pisi was highly inhibited by Phenamacril in vitro. This suggests thatdespite of the high degree of structural conservation in the myosin super-family, subtle differences render Phenamacril a highly specific and potent reversible inhibitor of Fusarium class I myosin.[1] Zheng Z, Yiping H, Yiqiang C et al (2015): Sci Rep, 5 (2021): 8248.[2] Zhang C, Yun C, Yanni Y et al (2015): Environ Microbiol, 17 (8): 2735–46.[3] Krishna C, Taft MH, Martin R et al (2011): J Biol Chem, 286 (34): 29700–708.