Final answer:
Rabs are proteins that recruit tethering proteins for vesicle targeting and they bind to lipids, enabling their association with membranes.
Step-by-step explanation:
Rabs are small proteins that play a pivotal role in vesicular transport within a cell. They are involved in recruiting tethering proteins to hold vesicles close to their target membranes in preparation for fusion. The question asks what Rabs bind to in this process. Among the options given, Rabs bind to lipids, allowing them to associate with the vesicular and target membranes. This lipid binding often involves post-translational modifications such as prenylation, where a lipid moiety like a farnesyl group is added to the protein, facilitating its attachment to the membrane.
In the context of the cell, proteins in the plasma membrane function to recognize specific molecules or particles, a process facilitated by the binding of proteins to lipids in the membrane. Rabs are part of the larger molecular machinery that ensures cargo is delivered to the correct location within or outside the cell. In summary, Rabs bind to lipids, allowing them to interact with and stabilize membranes, which is a critical step in vesicle tethering and fusion events.