Why is that important? Usher is a membrane part of two component system responsible for assembly and transport of fimbriae/pili in gram-negative bacteria – pretty essential element in these organisms. This protein was identified in early 90s (or even earlier) and for quite a while lots of people tried to solve/predict/model its structure. Its structure was assumed to resemble porin – but a large insert right in the middle of beta-barrel gave lots of problems in predicting correct topology. Now we know (at least my colleague saw it, we need to wait) how the final structure looks like and I was also told that its functional aspects have a big relevance to other secretion systems. Have a look on this protein when it’s out (I’ll post definitely about it) – I think you will be surprised even if nuances of host-pathogen interactions are not very appealing to you.

Studying any niche area on the molecular level can be very rewarding. Novel protein fold by itself is not a big deal anymore (it used to be – browse through archives of Nat. Struc. Biol. from several years ago). But putting this novel structure in well known functional context and understanding constrains that led to a new solution is still considered a first-class science.

This is from Nature Reviews Microbiology, and subscription may be required.

clipped from www.nature.com Recent evidence shows that mycobacteria have developed novel and specialized secretion systems for the transport of extracellular proteins across their hydrophobic, and highly impermeable, cell wall. Strikingly, mycobacterial genomes encode up to five of these transport systems. Two of these systems, ESX-1 and ESX-5, are involved in virulence — they both affect the cell-to-cell migration of pathogenic mycobacteria. Here, we discuss this novel secretion pathway and consider variants that are present in various Gram-positive bacteria. Given the unique composition of this secretion system, and its general importance, we propose that, in line with the accepted nomenclature, it should be called type VII secretion.

This nice ring of helices is a model of the molecular needle of type III secretion system (T3SS). This system is used by many bacterial species during an infection: attaching to the host cell is followed by a insertion of a needle into the host cell and transporting effector proteins directly into that cell. The model here is a combination of the crystal structure of the single subunit and 3D reconstruction of the needle from electron microscopy.

I believe that next years will bring more full atom models of important cell structures. It can be seen directly from the publications: certain research groups are solving structures of missing elements of the large protein complexes, one by one. The model above is for sure a one step closer to having the whole T3SS, including cytoplasmic, transmembrane and extracellular parts at a atomic resolution.

The paper about this model was published last year in PNAS (free access) by Janet E. Deane and Pietro Roversi et al. The model is deposited in the PDB as 2V6L. PubMed ID for the abstract is: 16888041.