Membrane enzymes hydrophobic interactions

As with other multisubunit enzymes (e.g., allosteric enzymes), the structural integrity of a membrane-bound enzyme primarily is maintained by noncovalent interactions such as hydrogen bonding, electrostatics, and hydrophobic interactions. Hydrophobic polypeptides (or hydrophobic portions of polypeptides) apparently are used to anchor the enzymes to the membrane through interactions with phospholipids. Therefore, I would characterize the interaction between the enzyme and membrane as chemical in nature rather than as geometric. ... 

A characteristic of virtually all methanogen hydrogenases is their very large native size (although they are soluble enzymes), typically 600-1000 kDa. This is often explained as a result of hydrophobic interactions with other proteins, and as an indication that it is a loosely-bound membrane protein. H2ase is often associated with membranes early during its purification [271,280]. These properties have been investigated in several ways by electron microscopy. 

Once the importance of hydrophobic interactions became generally evident, it became clear that these interactions might undergo important changes whenever proteins are exposed to low temperatures. This view dominates reports on multimeric enzyme systems, micelle-like aggregates, and membranous structures. I will refer to several examples from the relatively recent literature for purposes of illustration. 

In chloroplasts of higher plants the ferredoxin-thioredoxin system links light-triggered events in thylakoid membranes with the regulation of enzymes in the stroma (1,2). If the conformation of enzymes changes because of modulators action then the surface exposed to the solvent will be different from the native state (3). As a consequence, interactions of modified enzymes with supramolecular structures (membranes, protein complexes) will differ respect to native forms. Since thylakoid membranes are complex structures they are not adequate for uncovering molecular mechanisms that participate in protein interactions(4). In thfe respect, the well-defined structure of micelles of non-ionic detergents constitute model compounds for the analysis of hydrophobic interactions in proteins (5,6). We report herein that chloroplast fructose-1,6-bisphosphatase interacts with micelles of Triton X-114 in a pH-dependent process. 

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