A MAP6-Related Protein Is Present in Protozoa and Is Involved in Flagellum Motility

In vertebrates the microtubule-associated proteins MAP6 and MAP6d1 stabilize cold-resistant microtubules. Cilia and flagella have cold-stable microtubules but MAP6 proteins have not been identified in these organelles. Here, we describe TbSAXO as the first MAP6-related protein to be identified in a protozoan, Trypanosoma brucei. Using a heterologous expression system, we show that TbSAXO is a microtubule stabilizing protein. Furthermore we identify the domains of the protein responsible for microtubule binding and stabilizing and show that they share homologies with the microtubule-stabilizing Mn domains of the MAP6 proteins. We demonstrate, in the flagellated parasite, that TbSAXO is an axonemal protein that plays a role in flagellum motility. Lastly we provide evidence that TbSAXO belongs to a group of MAP6-related proteins (SAXO proteins) present only in ciliated or flagellated organisms ranging from protozoa to mammals. We discuss the potential roles of the SAXO proteins in cilia and flagella function

Distinct Roles of Phenol-Soluble Modulins in Spreading of Staphylococcus aureus on Wet Surfaces

<p>The human pathogen Staphylococcus aureus is renowned for the rapid colonization of contaminated wounds, medical implants, and food products. Nevertheless, little is known about the mechanisms that allow S. aureus to colonize the respective wet surfaces. The present studies were therefore aimed at identifying factors used by S. aureus cells to spread over wet surfaces, starting either from planktonic or biofilm-associated states. Through proteomics analyses we pinpoint phenol-soluble modulins (PSMs) as prime facilitators of the spreading process. To dissect the roles of the eight PSMs produced by S. aureus, these peptides were chemically synthesized and tested in spreading assays with different psm mutant strains. The results show that PSM alpha 3 and PSM gamma are the strongest facilitators of spreading both for planktonic cells and cells in catheter-associated biofilms. Compared to the six other PSMs of S. aureus, PSM alpha 3 and PSM gamma combine strong surfactant activities with a relatively low overall hydropathicity. Importantly, we show that PSM-mediated motility of S. aureus facilitates the rapid colonization of wet surfaces next to catheters and the colonization of fresh meat.</p>

Molecular architecture of axonemal microtubule doublets revealed by cryo-electron tomography

The axoneme, which forms the core of eukaryotic flagella and cilia, is one of the largest macromolecular machines with a structure that is largely conserved from protists to mammals. Microtubule doublets are structural components of axonemes containing a number of proteins besides tubulin, and are usually found in arrays of nine doublets arranged around two singlet microtubules. Coordinated sliding of adjacent doublets, which involves a host of other proteins in the axoneme, produces periodic beating movements of the axoneme. We have obtained a 3D density map of intact microtubule doublets using cryo-electron tomography and image averaging. Our map, with a resolution of about 3 nm, provides insights into locations of particular proteins within the doublets and the structural features of the doublets that define their mechanical properties. We identify likely candidates for several of these non-tubulin components of the doublets. This work offers novel insight on how tubulin protofilaments and accessory proteins attach together to form the doublets and provides a structural basis for understanding doublet function in axonemes