PubMed · 7911076
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T L Whiteside. 1994. Symposium-in-writing. Introduction.. https://doi.org/10.1006/clin.1994.1079
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The SUMO family in vertebrates includes at least three distinct proteins (SUMO-1, -2, and -3) that are added as post-translational modifications to target proteins. A considerable number of SUMO-1 target proteins have been identified, but little is known about SUMO-2. A stable HeLa cell line expressing His6-tagged SUMO-2 was established and used to label and purify novel endogenous SUMO-2 target proteins. Tagged forms of SUMO-2 were functional and localized predominantly in the nucleus. His6-tagged SUMO-2 conjugates were affinity-purified from nuclear fractions and identified by mass spectrometry. Eight novel potential SUMO-2 target proteins were identified by at least two peptides. Three of these proteins, SART1, heterogeneous nuclear ribonucleoprotein (RNP) M, and the U5 small nuclear RNP 200-kDa helicase, play a role in RNA metabolism. SART1 and heterogeneous nuclear RNP M were both shown to be genuine SUMO targets, confirming the validity of the approach.
Lectins from legumes constitute one of the most thoroughly studied families of proteins, yet the absence of a rigorous framework to explain their carbohydrate binding specificities appears to have prevented a rational approach to alter their ligand binding activity. Studies reported here deal with the redesign of the recognition propensity of peanut agglutinin (PNA), an important member of the family. PNA is extensively used as a tool for recognition of the tumor-associated Thomsen-Friedenrich antigen (T-antigen; Galbeta1-3GalNAc) on the surfaces of malignant cells and immature thymocytes. PNA also recognizes N-acetyllactosamine (LacNAc; Galbeta1-4GlcNAc), which is present at the termini of several cell-surface glycoproteins. The crystal structure of the PNA-lactose complex revealed, in addition to the expected interactions with the residues constituting the binding site, the presence of leucine 212 at a position close enough to be in steric contact with the acetamido group on LacNAc. We report here two leucine mutants, one to asparagine (L212N) and the other to alanine (L212A), that exhibit distinct preference for T-antigen and N-acetyllactosamine, respectively. Carbohydrate binding studies reveal that mutant L212N does not recognize LacNAc at high concentrations, thus making it an exquisitely specific cell-surface marker compared with its wild-type counterpart.
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