Which type of protein modification increases stability and directs protein traffic?

Glycosylation is the process that increases the stability of proteins and directs their trafficking. This post-translational modification involves the addition of carbohydrate moieties (sugars) to proteins, which can significantly affect their folding, stability, and interaction with other cellular molecules.

The addition of carbohydrates can protect proteins from degradation by proteolytic enzymes, enhancing their half-life within the cell. Moreover, glycosylation plays a crucial role in the proper localization of proteins; it can determine the proteins' destination within the secretory pathway, such as guiding them to the plasma membrane, lysosomes, or being secreted outside the cell. The specific sugar residues added can also serve as signals that are recognized by lectins and other pathway-specific receptors, ensuring that proteins are delivered to the correct cellular compartments.

While phosphorylation, acetylation, and methylation also play important roles in protein function and regulation, they do not primarily serve the dual purpose of increasing protein stability and directing trafficking in the same way that glycosylation does.