Interactions between the Microtubule Binding Protein EB1 and F-Actin

Many cellular processes including cell division and cell migration require coordination between the actin and microtubule (MT) cytoskeletons. This coordination is as-yet poorly understood, but proteins such as formins and IQGAP1 are known to be involved. We show that the MT binding protein EB1 (end-binding protein 1), a key regulator of MT dynamics, can bind directly to filamentous actin (F-actin) F-actin. We determined that the EB1:F-actin interaction is salt sensitive and weak under physiological salt concentrations but might be relevant in contexts where the local concentration of actin is high. Using bioinformatics and mutagenesis, we found that the EB1:F-actin binding site partially overlaps the well-characterized EB1:MT binding interface. Congruently, competition experiments indicate that EB1 can bind to F-actin or MTs but not both simultaneously. These observations suggest that EB1:F-actin interactions may negatively regulate EB1:MT interactions, and we speculate that this interaction may assist cells in differentially regulating MT stability in the actin-rich cortex as opposed to the cell interior.