Revealing biophysical properties of KfrA-type proteins as a novel class of cytoskeletal, coiled-coil plasmid-encoded proteins

Immunolocalization and 3D modeling of three unique proteins belonging to the costa of Tritrichomonas foetus

Nowadays, even in light of all the massive advances in cell biology, we still find some cellular structures that are not entirely understood. Among those, we highlight the costa, a structure from the mastigont system existent only in some members of the orders Trichomonadida and Tritrichomonadida, including the pathogens of venereal diseases in humans and cattle, Trichomonas vaginalis (T. vaginalis) and Tritrichomonas foetus (T. foetus), respectively. The costa is a prominent striated fiber and, although part of the cytoskeleton, differs from its classical components, and its molecular composition is still not fully characterized. Using proteomics of T. foetus's costa fraction, we previously identified hypothetic proteins, and among these, the protein ARM19800.1 positively localized in the costa and named costain-1. In this study, two other protein candidates were analyzed. To achieve the specific localization of 11810 and 32137 proteins in T. foetus's cells, it was used expansion microscopy and immunocytochemistry. The immunofluorescence revealed the presence of both proteins throughout the whole costa but with different intensities. Immunocytochemistry using negative staining, LR-White, and Epon embedding revealed further analyses of the protein's localization. All techniques confirmed the distinct and distributed localization of both proteins: costain-2 (11810) and costain-3 (32137). Also, AlfaFold3 was used to generate 3D models of the three identified proteins, showing a major prevalence of α-helical spans. Nonetheless, the identification and further characterization of these unique proteins can help understand their functional role in the assembled costa and, therefore, better understand the organization and function of this structure in these organisms.

A Plasmid Carrying blaIMP-56 in Pseudomonas aeruginosa Belonging to a Novel Resistance Plasmid Family

bla_IMP and bla_VIM are the most detected plasmid-encoded carbapenemase genes in Pseudomonas aeruginosa. Previous studies have reported plasmid sequences carrying bla_IMP variants, except bla_IMP-56. In this study, we aimed to characterize a plasmid carrying bla_IMP-56 in a P. aeruginosa strain isolated from a Mexican hospital. The whole genome of P. aeruginosa strain PE52 was sequenced using Illumina Miseq 2 × 150 bp, with 5 million paired-end reads. We characterized a 27 kb plasmid (pPE52IMP) that carried bla_IMP-56. The phylogenetic analysis of RepA in pPE52IMP and 33 P. aeruginosa plasmids carrying resistance genes reported in the GenBank revealed that pPE52IMP and four plasmids (pMATVIM-7, unnamed (FDAARGOS_570), pD5170990, and pMRVIM0713) were in the same clade. These closely related plasmids belonged to the MOB_P11 subfamily and had similar backbones. Another plasmid (p4130-KPC) had a similar backbone to pPE52IMP; however, its RepA was truncated. In these plasmids, the resistance genes bla_KPC-2, bla_VIM variants, aac(6′)-Ib4, bla_OXA variants, and bla_IMP-56 were inserted between phd and resolvase genes. This study describes a new family of plasmids carrying resistance genes, with a similar backbone, the same RepA, and belonging to the MOB_P11 subfamily in P. aeruginosa. In addition, our characterized plasmid harboring bla_IMP-56 (pPE52IMP) belongs to this family.

Alpha-Helical Protein KfrC Acts as a Switch between the Lateral and Vertical Modes of Dissemination of Broad-Host-Range RA3 Plasmid from IncU (IncP-6) Incompatibility Group

KfrC proteins are encoded by the conjugative broad-host-range plasmids that also encode alpha-helical filament-forming KfrA proteins as exemplified by the RA3 plasmid from the IncU incompatibility group. The RA3 variants impaired in kfrA, kfrC, or both affected the host's growth and demonstrated the altered stability in a species-specific manner. In a search for partners of the alpha-helical KfrC protein, the host's membrane proteins and four RA3-encoded proteins were found, including the filamentous KfrA protein, segrosome protein KorB, and the T4SS proteins, the coupling protein VirD4 and ATPase VirB4. The C-terminal, 112-residue dimerization domain of KfrC was involved in the interactions with KorB, the master player of the active partition, and VirD4, a key component of the conjugative transfer process. In Pseudomonas putida, but not in Escherichia coli, the lack of KfrC decreased the stability but improved the transfer ability. We showed that KfrC and KfrA were involved in the plasmid maintenance and conjugative transfer and that KfrC may play a species-dependent role of a switch between vertical and horizontal modes of RA3 spreading.