Biology subjects

Grubic, T.

Publications and source records attributed to Grubic, T..

3 recordsLinked to original sources

bioRxiv2026

Low-affinity binding motif in microtubule plus-end condensates specializes microtubule function

The microtubule plus-end tracking proteins (+TIPs) CLIP-170/Bik1 and EB/Bim1 form a condensate, the +TIP body, at the plus-end of most microtubules in vivo. Remarkably, however, these +TIP bodies typically impart different dynamics and interaction profiles to distinct microtubules, according to their cellular function. The molecular mechanisms underlying the functional versatility of the +TIP body are unknown. Here, we show that the +TIP Kar9 utilizes repeats of a lysine-aspartate-lysine (KDK)-centered short linear motif (SLiM) to interact with Bik1 on a restricted subset of cytoplasmic microtubules during yeast mitosis. Furthermore, these multivalent Kar9-Bik1 interactions tune the material behavior of the +TIP body to specify proper microtubule function. Indicating that KDK serves as generic Bik1-interaction motif, similar motifs are also present in Kip2, where they mediate Bik1-dependent recruitment of Kip2 to the +TIP body. Together, our study provides insights into how low-affinity Bik1 interactors diversify microtubule function by locally specializing the content and behavior of +TIP bodies.

Cell Biology↗

bioRxiv2026

Metabolites Shift Equilibria of Biomolecular Condensates

Biomolecular condensates compartmentalize biochemistry in living cells. While in vitro models of condensates involve only a few components, the cytoplasm is a complex mixture with thousands of components, including many small molecules. While many macromolecular drivers of phase separation have been revealed, the contributions from small molecules have received little attention. To quantify the impact of solutes on biomolecular condensates, we introduce susceptibility, a dimensionless descriptor of condensate response to solute perturbations. We measured how three model condensates, assembled by distinct cohesive mechanisms, respond to diverse solutes including amino acids and nucleotides. Generically, solutes shift condensate phase equilibria, with susceptibilities spanning over four orders of magnitude. These values reflect underlying molecular interactions, consistent with theoretical descriptions including Flory-Huggins and polyphasic linkages. As one example of the predictive power of susceptibility, we exploit enzymatic activity to induce condensation and modulate material properties. Our work establishes susceptibility as an indicator of the sensitivity of biomolecular condensates to solutes, with implications for cell physiology and therapeutic design. SIGNIFICANCE STATEMENTCells compartmentalize biochemistry using biomolecular condensates formed through phase separation. Although cells contain thousands of small molecules, little is known about their influence on condensation. In such complex mixtures, mapping full phase diagrams is infeasible. Alternatively, we introduce susceptibility to characterize system response around a working composition. Using three distinct model condensates and over a dozen solutes, we observe susceptibilities varying over four orders of magnitude. We provide a general thermodynamic framework that clarifies the driving forces behind these responses, rationalizing their magnitude and their dependence on location in the phase diagram. Our work provides a framework for understanding and harnessing solutes to regulate biomolecular condensation, with implications for cell physiology and therapeutic design.

biophysics↗

bioRxiv2024

Phase separation of a microtubule plus-end tracking protein into a fluid fractal network

Microtubule plus-end tracking proteins (+TIPs) are involved in virtually all microtubule-based cellular processes, and it has been recently proposed that they function as liquid condensates. However, the formation process and internal organization of +TIP condensates are poorly understood. Here, we have investigated the phase separation of the CLIP-170 family member Bik1, a key +TIP implicated in budding yeast cell division. We found that Bik1 is a rod-shaped dimer whose conformation is dominated by its central coiled-coil domain. Liquid condensation is accompanied by Bik1 conformational rearrangements, leading to a 2-3-fold rise in interactions between the proteins folded and disordered domains. In contrast to classical liquids, the supramolecular structure of the Bik1 condensate is heterogeneous, with a fractal structure of protein-rich and protein-free domains. This observation provides structural evidence in support of recent models of biomolecular condensates based on percolation. More broadly, our results provide insights into the structure, dynamic rearrangement, and organization of a complex, multidomain protein in its dilute and condensed phases. Our experimental framework can be extended to other biomolecular condensates, including more intricate +TIP networks.

biochemistry↗