Which type of modification involves attaching a small protein to another protein to influence its function?

The concept being addressed in this question pertains to post-translational modifications of proteins, which are crucial in altering protein functions, localization, and interactions. The modification that specifically involves attaching a small protein to another protein is known as SUMOylation.

SUMOylation stands for Small Ubiquitin-like Modifier (SUMO) attachment. This process involves the conjugation of SUMO proteins to target proteins, influencing their stability, localization, and interaction with other proteins. It can alter the protein's activity, affecting cellular processes like transcription, DNA repair, and signal transduction. SUMOylation is particularly important in regulating protein interactions and can modulate pathways that are involved in stress responses or cell cycle control.

The other types of modifications mentioned, such as acetylation, phosphorylation, and methylation, involve different molecular alterations that do not include the attachment of a small protein. For example, acetylation typically introduces an acetyl group to lysine residues, affecting protein structure and function. Phosphorylation involves the addition of phosphate groups, often altering enzymatic activity or signaling pathways. Methylation can add methyl groups, which also affect gene expression and protein function but do not include the conjugation of a protein like SUM