Regulation and Function of SUMO Modification

Abstract

Small ubiquitin-like modifier (SUMO) 1 is a protein of 97 amino acids that is structurally similar to ubiquitin and has been called by other names including Smt3p, Pmt2p, PIC-1, GMP1, Ubl1, and Sentrin (1). Like ubiquitin, SUMO has been found to be covalently attached to certain lysine residues of specific target proteins (2). In contrast to ubiquitination, however, sumoylation does not promote the degradation of proteins but instead alters a number of different functional parameters of proteins, depending on the protein substrate in question. These parameters include but are not limited to properties such as subcellular localization, protein partnering, and DNA-binding and/or transactivation functions of transcription factors (2-4). The contrast between the functional effects of ubiquitination and sumoylation is most striking in the case of IKB, where sumoylation stabilizes the protein by modifying the same residue that is ubiquitinated, thereby directly competing with that pathway (5). This review will focus on the regulation of SUMO modification and its role in controlling the functional properties of proteins. The reader is also referred to other excellent reviews on this topic (2-4, 6-8).