Examining Part–Part Interactions Toward Improving Mechanistic Explanations in Cell Biology

Abstract This paper’s aim is to provide a normative notion of relative completeness that pinpoints cell-biological part–part interactions as a critical niche for the integration of mechanistic explanations with the explanatory features of lawlike generalizations. Using a critiquing account of mechanisms that determines whether and how a given mechanistic explanation could become relatively more complete, I highlight the critical role of part–part interactions in the cell. Mechanistic explanations, which are a mainstay of causal accounts in cell biology, are underpinned in large part by a network of such interactions (e.g. protein–protein or protein–nucleic-acid). In studies that attempt to discover these interactions, there is a tacit assumption that an ‘interaction’ is constituted simply by the proximity between and/or enzymatic changes imparted on the interacting parts. As very few substantive theoretical accounts of what may actually constitute an ‘interaction’ in the context of the cell have been put forth, I develop an account of protein–protein interactions (a key type of part–part interactions in the cell with implications for other types of cellular interactions) toward making the explanation more complete. In doing so, I first map out four aspects relevant to the sequence of events taking place in at least a significant proportion of protein–protein interactions, and, second, propose (i) interaction-enabling properties of proteins and (ii) interaction-enabling properties of the proteins’ environment as elements that could be explained by relevant lawlike generalizations. These generalization-based explanations could answer contrastive why-this-and-not-that type of questions pertaining to different aspects of a protein–protein interaction of interest in a mechanistic explanation, which would otherwise be difficult to answer in cell-biological mechanistic terms. This approach illustrates how part–part interactions in a mechanism could be explained by lawlike generalizations, with the eventual goal of making the overall explanation more fruitful and informative.