 Proteins can bind to other proteins as well as to small @-@ molecule substrates . When proteins bind specifically to other copies of the same molecule , they can <unk> to form fibrils ; this process occurs often in structural proteins that consist of globular monomers that self @-@ associate to form rigid fibers . Protein – protein interactions also regulate enzymatic activity , control progression through the cell cycle , and allow the assembly of large protein complexes that carry out many closely related reactions with a common biological function . Proteins can also bind to , or even be integrated into , cell membranes . The ability of binding partners to induce conformational changes in proteins allows the construction of enormously complex signaling networks . <unk> , as interactions between proteins are <unk> , and depend heavily on the availability of different groups of partner proteins to form <unk> that are capable to carry out discrete sets of function , study of the interactions between specific proteins is a key to understand important aspects of cellular function , and ultimately the properties that distinguish particular cell types . 
