TM helices are an important structural aspect of proteinmembrane interactions . They are stabilized by such factors as hydrophobic matching (the length matching of helix and membrane hydrophobic spans), or the degree of charge/polarity of the helix's termini. The fluid nature of interactions between proteins and membranes further means that either component can adapt to non-optimal characteristics : among other changes, excessively long helices -particularly if monomeric or at low degrees of oligomerization -will frequently tilt to better accommodate their hydrophobic span within the membrane core; at the same time, lipids vicinal to the protein may display a thicker bilayer profile, with a concomitant locally thicker core. Conversely, very short helices can induce a local thinning of membranes.