Inhibition of respiratory complex I (CI) is becoming a promising anti-cancer strategy, encouraging the design and the use of inhibitors, whose mechanism of action, efficacy and specificity remain elusive. As CI is a central player of cellular bioenergetics, a finely tuned dosing of targeting drugs is required to avoid side effects. We compared the specificity and mode of action of CI inhibitors metformin, BAY 87-2243 and EVP 4593 using cancer cell models devoid of CI. Here we show that both BAY 87-2243 and EVP 4593 were selective, while the antiproliferative effects of metformin were considerably independent from CI inhibition. Molecular docking predictions indicated that the high efficiency of BAY 87-2243 and EVP 4593 may derive from the tight network of bonds in the quinone binding pocket, although in different sites. Most of the amino acids involved in such interactions are conserved across species and only rarely found mutated in human. Our data make a case for caution when referring to metformin as a CI-targeting compound, and highlight the need for dosage optimization and careful evaluation of molecular interactions between inhibitors and the holoenzyme.

Polyhydroxybutyrate (PHB) is a biodegradable natural polymer produced by different prokaryotes as a valuable carbon and energy storage compound. Its biosynthesis pathway requires the sole expression of the phaCAB operon, although auxiliary genes play a role in controlling polymer accumulation, degradation, granule formation and stabilization. Due to its biodegradability, PHB is currently regarded as a promising alternative to synthetic plastics for industrial/biotechnological applications. Azohydromonas lata strain H1 has been reported to accumulate PHB by using simple, inexpensive carbon sources. Here, we present the first de novo genome assembly of the A. lata strain H1. The genome assembly is over 7.7 Mb in size, including a circular megaplasmid of approximately 456 Kbp. In addition to the phaCAB operon, single genes ascribable to PhaC and PhaA functions and auxiliary genes were also detected. A comparative genomic analysis of the available genomes of the genus Azohydromonas revealed the presence of phaCAB and auxiliary genes in all Azohydromonas species investigated, suggesting that the PHB production is a common feature of the genus. Based on sequence identity, we also suggest A. australica as the closest species to which the phaCAB operon of the strain H1, reported in 1998, is similar.

Polyhydroxybutyrate (PHB) is a biodegradable natural polymer produced by different prokaryotes as a valuable carbon and energy storage compound. Its biosynthesis pathway requires the sole expression of the phaCAB operon, although auxiliary genes play a role in controlling polymer accumulation, degradation, granules formation and stabilisation. Due to its biodegradability, PHB is currently regarded as a promising alternative to synthetic plastics for industrial/biotechnological applications. Azohydromonas lata strain H1 has been reported to accumulate PHB by using simple, inexpensive carbon sources. Here we present the first de novo genome assembly of the A. lata strain H1. The genome assembly is over 7.7Mb in size including a circular megaplasmid of approximately 456Kbp. In addition to the phaCAB operon, single genes ascribable to PhaC and PhaA functions and auxiliary genes were also detected. A comparative genomic analysis of the available genomes of the genus Azohydromonas revealed the presence of phaCAB and auxiliary genes in all Azohydromonas species investigated, suggesting the PHB production is a common feature of the genus. Based on sequence identity, we also suggest A. australica as the closest species to which the phaCAB operon of the strain H1 reported in 1998 is similar.