Intracellular transport

Tuberin-dependent membrane localization of polycystin-1: a functional link between polycystic kidney disease and the TSC2 tumour suppressor gene. Kleymenova, E. et al. Mol. Cell 7 , 823–832 (2001) [PubMed]

Mutation of the PKD1 gene is responsible for ∼85% of cases of autosomal dominant polycystic kidney disease. 63 bp upstream of PKD1 is the tuberous sclerosis 2 (TSC2) tumour-suppressor gene, and a functional link between the PKD1 gene product — polycystin-1 — and the TSC2 product, tuberin, has now been made. Kleymenova et al. show that, in tuberin-deficient cells, intracellular trafficking of polycystin-1 is disrupted, implicating tuberin as a determinant in the functional localization of polycystin-1.

Exocytosis

SNAREs are concentrated in cholesterol-dependent clusters that define docking and fusion sites for exocytosis. Lang, T. et al. EMBO J. 20 , 2202–2213 (2001) [PubMed]

SNARE proteins are highly enriched in lipid rafts in PC12 cells: implications for the spatial control of exocytosis. Chamberlain, L. H. et al. Proc. Natl Acad. Sci. USA 98 , 5619–5624 (2001) [PubMed]

Pairing of cognate SNARE proteins on vesicles and target membranes is believed to be the molecular basis for membrane fusion. It is suspected that several trans-SNARE complexes take part in this interaction, but this has not been documented. Two papers now show that SNARE proteins are concentrated in cholesterol-rich microdomains on the plasma membrane, and that their association with these domains is important for exocytosis. This supports the concept that SNARE complexes are organized spatially for efficient membrane fusion.

Technology

Protein quantification from complex protein mixtures using a proteomics methodology with single-cell resolution. Zhang, H. T. et al. Proc. Natl Acad. Sci. USA 98 , 5497–5502 (2001) [PubMed]

Immunodetection amplified by T7 RNA polymerase (IDAT) — a new technique for protein quantification — is at least 109 times more sensitive than the most sensitive ELISA technique available today. The technique consists of coupling double-stranded oligonucleotides containing the T7 promoter covalently to antibodies against a given antigen, amplifying RNA from the oligonucleotides with T7 RNA polymerase and quantifying the radioactive reaction product. The method is more sensitive than immuno-PCR, and it is also more accurate owing to the linearity of the amplification reaction by T7 RNA polymerase. The authors suggest that the method has potential as an automated detection system for chip-based proteomics.