Insertion of helix-forming segments into the membrane and their association determines

Insertion of helix-forming segments into the membrane and their association determines the structure function and expression levels of all plasma membrane proteins. differences among these residues. AZD0530 Finally we derive comprehensive mutational landscapes in the membrane domains of Glycophorin A and the ErbB2 oncogene and find that insertion and self-association are strongly coupled in receptor homodimers. DOI: http://dx.doi.org/10.7554/eLife.12125.001 could grow on a common antibiotic called ampicillin if it had enough of an antibiotic-degrading enzyme called β-lactamase anchored into its inner membrane. Now Elazar et al. have used this enzyme to obtain detailed information on the interactions between a biological membrane and a membrane protein. First hundreds of different mutations were introduced into the gene that encodes the enzyme to generate a population of bacteria that each had AZD0530 a slightly different membrane anchor. The mutant bacteria were then grown in the presence of the antibiotic meaning that those mutants with a more stable membrane anchor were more likely to survive and grow than those with less stable anchors. Elazar et al. then collected all AZD0530 the surviving bacteria sequenced their DNA and AZD0530 measured how common the different mutations were in the final population. This approach was less labor-intensive and more accurate than traditional methods for monitoring membrane-anchored proteins and the resulting large dataset was used to uncover which features affect a protein’s stability in a membrane. These results also showed that a biological membrane’s core is considerably more hydrophobic than AZD0530 was previously thought. In addition to being hydrophobic biological membranes have more negative charge in the side that faces into the cell. This means that membrane proteins with a positive charge in this region will be more stable and Elazar et al. were able AZD0530 to use their new system to measure this effect for the first time. Finally membrane proteins do not only span the membrane; they also bind with other membrane proteins in order to carry out their roles. Elazar et al. used their system to look at the surfaces of human membrane proteins that interact with one another and build a detailed map of the interaction surfaces from which they derived accurate models of the membrane proteins. Overall these new findings could now be used to model the three-dimensional structures of membrane proteins and improve their stability. This in turn may help efforts to develop these proteins into more robust experimental tools and in the search for drugs that target membrane proteins. DOI: http://dx.doi.org/10.7554/eLife.12125.002 Introduction The past four decades have seen persistent efforts to decipher the contributions to membrane-protein energetics?(Reynolds et al. 1974 Cymer et al. 2015 Membrane-protein folding can be conceptually divided into two thermodynamic stages?(Popot and Engelman 1990 Cymer et al. 2015 each of which affects membrane-protein structure function and expression levels: the insertion into the membrane of transmembrane segments as α helices and their association to form helix bundles?(Ben-Tal et al. 1996 Heinrich and Rapoport 2003 Moll and Thompson 1994 White and Wimley 1999 Popot and Engelman 1990 While significant progress has been made in structure prediction design and engineering of soluble proteins?(Fleishman and Baker 2012 important but fewer successes were reported in design of membrane proteins?(Joh et al. 2014 Li et al. 2004 largely owing to the complexity of the plasma membrane and the lack of systematic and accurate measurements of membrane-protein energetics?(Cymer et al. 2015 Recently experimental systems that offer a realistic model for biological membranes have advanced. von Heijne and co-workers quantitated the partitioning of engineered peptides fused to the bacterial transmembrane protein leader peptidase (Lep) Pdpn between membrane-inserted and translocated states and highlighted the importance of interactions between the translocon and the nascent polypeptide chain in determining partitioning?(Hessa et al. 2007 ?jemalm et al. 2013 The insertion energetics obtained from this assay however were significantly lower than expected from previous theoretical and experimental studies; for instance the apparent atomic-solvation parameter which quantifies the free-energy contribution from the partitioning of hydrophobic.