"Moving through mucus", "quick death-tagging" and more, in my picks of the week from RB

Another week has gone by and some very interesting molbio blog posts have been aggregated to Researchblogging.org. Every week [see my opening post on the matter], I'll select some blog posts I consider particularly interesting in the field of molecular biology [see here to get a sense of the criteria that will be used], briefly describe them and list them here for you to check out.

Note that I'm only taking into consideration the molbio-related blog posts aggregated under "Biology".

Congratulations to everyone who got their post selected.

1) Helicobacter pylori is a gram-negative bacterium that colonizes the epithelium of the human stomach. Although most of the infected individuals are asymptomatic (~80%), it can cause peptide ulcers and gastric cancer.

H. pylori can survive in the highly acidic environment of the human stomach through a urease-dependent mechanism. On his first appearance at Picks of the Week, Tim Sampson at Blogging for Bacteriophages discusses a recent article shedding light on the mechanism that allows this bacterial pathogen to move through the viscoelastic mucus gel that coats the stomach wall, an important aspect of its pathogenesis.
Apparently, its motility is directly related to the mechanism with which it copes with low pH.

2) The ubiquitin-proteasome system is the major cytosolic proteolytic system in eukaryotes and plays important functions in different aspects of cell biology, like cell cycle control, apoptosis, inflammation, signal transduction, protein quality control, and many others. Basically, it degrades proteins that have been modified by the attachment of a chain of ubiquitin molecules, and this latter process occurs through a series of steps.

An unanswered question has been how this works. Is the ubiquitin chain formed first, and then transferred to the target en bloc? Or are single ubiquitin transferred one at a time, sequentially, first to the target protein and then to the previously-attached ubiquitins?

Ian York at Mystery Rays from Outer Space, briefly comments on an impressive new article reporting the “detection of sequential polyubiquitylation on a millisecond timescale”. The authors show, by measurements with millisecond time resolution, that substrate polyubiquitylation proceeds sequentially, that is, one at a time.

3. It is now generally accepted that mitochondria are dynamic organelles, constantly undergoing both divisions and fusions. Interestingly, mutations in genes involved in such processes can lead to neurodegenerative diseases. LabRat (on her 4th Pick in a row!) gives a brief overview of the mechanisms underlying its dynamic nature.

That's it for this week. Stay tuned for more MolBio Research Highlights!

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Some of the articles discussed in this week's selected posts:

Celli, J., Turner, B., Afdhal, N., Keates, S., Ghiran, I., Kelly, C., Ewoldt, R., McKinley, G., So, P., Erramilli, S., & Bansil, R. (2009). Helicobacter pylori moves through mucus by reducing mucin viscoelasticity Proceedings of the National Academy of Sciences, 106 (34), 14321-14326 DOI: 10.1073/pnas.0903438106

Pierce, N., Kleiger, G., Shan, S., & Deshaies, R. (2009). Detection of sequential polyubiquitylation on a millisecond timescale Nature, 462 (7273), 615-619 DOI: 10.1038/nature08595

Benard G, & Karbowski M (2009). Mitochondrial fusion and division: Regulation and role in cell viability. Seminars in cell & developmental biology, 20 (3), 365-74 PMID: 19530306