Enolase 1 (ENO1), or alpha enolase, is a glycolytic enzyme with a highly interesting subcellular localization profile. In the subcellular section of the Human Protein Atlas, it is apparent that alpha enolase can be found both in the cytosol, at the plasma membrane and in the nucleus, making it one of thousands of multi-localizing proteins.

Alpha enolase is a well-known example of a moonlighting protein. Such proteins can performs different functions depending on cellular context, such as in different compartments of the cell, and are often metabolic enzymes (PMID: 37093283).

In the cytosol, alpha enolase has a major role as an enzyme in glycolysis, but it also acts in several non-canonical roles in other compartments of the cell (PMID: 36402937). For example, an alternatively spliced form of alpha enolase in the nucleus functions as a transcriptional inhibitor and tumor suppressor, while alpha enolase has been identified to act as a receptor and activator for plasminogen at the plasma membrane. This functional plasticity establishes ENO1 as a regulator in a wide variety of biological processes, including metabolism, apoptosis, myogenesis, plasmin activity, plasminogen activation, and tumorigenesis.

In an additional layer of complexity, we have observed that the expression, as well as the relative distribution of alpha enolase between cellular compartments, varies between individual cells, even in isogenic cell populations grown under the same conditions. Previous studies revealed that the expression heterogeneity of alpha enolase occurs independent of the cell cycle (PMID:33627808). This raises the question of a role for proteins like alpha enolase in establishing phenotypically diverse cellular states in human cell lines and tissues. In a current study, we are exploring the spatial complexity of the metabolic proteome, established by enzyme multi-localization and expression heterogeneity to shine light on this question.