This result validated our criteria for the in silico identification of Inc proteins. In spite of their ability to be recognized as TTS substrates, many putative Inc sellectchem pro teins are not detected at the inclusion membrane during in vitro culture, suggesting that their translocation might be controlled by an unknown mechanism. Results Inc protein hydrophobic domains consist of two transmembrane alpha helices The hallmark of Inc proteins is a large hydrophobic domain of 40 to 60 residues with non Inhibitors,Modulators,Libraries hydrophobic resi dues in its middle, resulting in a bilobal pattern on hydropathy plots. While it is assumed that this hydrophobic domain serves as an anchor in the inclusion membrane, its secondary structure has not been investi gated. The most common Inhibitors,Modulators,Libraries secondary structure for trans membrane segments is the alpha helix.

Inhibitors,Modulators,Libraries other structures include short buried hydrophobic helices or beta barrels. We submitted the sequences of 31 known Inc pro teins to Split analysis, which predicts the secondary structure of the transmembrane domains of membrane proteins. In all cases, Split analysis pre dicted that Inc protein hydrophobic domains correspond to two alpha helical transmembrane segments, ranging from 15 to 32 residues, connected with a short loop of 3 to 22 residues. The proximity of two helical segments suggested that they might constitute transmembrane helical hairpins, which consist of two closely spaced transmembrane helices separated by a tight turn loop with charged resi dues in the flanking regions.

To test this hypoth esis, the sequences of known Inc proteins were submitted to Topcons, which established a consensus prediction of membrane protein topology based on dif ferent programs and allowed us to define the limits of the helices and of the loop. Amino acids found in the loop between the helices were then subjected to the turn propensity scale of helical hairpins. Inhibitors,Modulators,Libraries Residues known as turn forming residues were enriched in the loop. Interestingly, helix breaking Pro and Gly residues were over represented as were the polar amino acid Asn and semi polar Ser and Thr residues, whereas high turn forming charged residues Lys, Arg, Asp, Glu were absent. In conclusion, the length and composition of Inhibitors,Modulators,Libraries known Inc proteins are compatible selleck chemicals llc with the topology observed for transmembrane domains separated by a loop. Loop length was on average of 8 residues, however a minority of Inc proteins such as IncB and IncC pre sented a notably longer loop. Most Inc proteins identified so far have only one transmembrane helical hairpin, with the exception of CT147, CT288 and CT850, which have two.