Distinctive properties of Arabidopsis SUMO paralogues support the in vivo predominant role of AtSUMO1/2 isoforms

Abstract

Protein modification by SUMO (small ubiquitin-related modifier) has emerged as an essential regulatory mechanism in eukaryotes. Even though the molecular mechanisms of SUMO conjugation/deconjugation are conserved, the number of SUMO machinery components and their degree of conservation are specific to each organism. In the present paper, we show data contributing to the notion that the four expressed Arabidopsis SUMO paralogues, AtSUMO1, 2, 3 and 5, have functionally diverged to a higher extent than their human orthologues. We have explored the degree of conservation of these paralogues and found that the surfaces involved in E1-activating enzyme recognition, and E2-conjugating enzyme and SIM (SUMO-interacting motif) non-covalent interactions are well conserved in AtSUMO1/2 isoforms, whereas AtSUMO3 shows a lower degree of conservation, and AtSUMO5 is the most divergent isoform. These differences are functionally relevant, since AtSUMO3 and 5 are deficient in establishing E2 non-covalent interactions, which has not been reported for any naturally occurring SUMO orthologue. In addition, AtSUMO3 is less efficiently conjugated than AtSUMO1/2, and AtSUMO5 shows the lowest conjugation level. A mutagenesis analysis revealed that decreases in conjugation rate and thioester-bond formation are the result of the non-conserved residues involved in E1-activating enzyme recognition that are present in AtSUMO3 and 5. The results of the present study support a role for the E1-activating enzyme in SUMO paralogue discrimination, providing a new mechanism to favour conjugation of the essential AtSUMO1/2 paralogues.

Defining the SUMO System in Maize: SUMOylation Is Up-Regulated during Endosperm Development and Rapidly Induced by Stress

“…S1), argues that the noncanonical forms have a function that involves their covalent attachment to other proteins, despite a less constrained primary sequence. In support, we detected modest sequence conservation among the noncanonical SUMOs within a region predicted to bind the SCE1 E2 noncovalently (Castaño-Miquel et al, 2011), suggesting that this association has been retained, especially with respect to the cereal isoforms (Supplemental Fig. S1).…”

“…And while conjugation could be demonstrated for Arabidopsis SUMO3 and SUMO5 using purified components and extended reaction times (Castaño-Miquel et al, 2011), it remains unclear if this conjugation is relevant in planta. Here, we failed to detect conjugation for recombinant maize SUMO2, likely due to the insolubility of the protein when expressed in E. coli.…”

Overexpression of SIZ1 enhances tolerance to cold and salt stresses and attenuates response to abscisic acid in Arabidopsis thaliana

“…SUM1 and SUM2 are functionally equivalent and are capable of forming poly-SUMO chains, whereas SUM3 does not perform this function. According to SUMO profiles, SUM1/2 and SUM3 have different specificities and possibly different targets (Castano-Miquel et al 2011;Kurepa et al 2003). SUMO is covalently conjugated to a target protein through a three-step cascade via E1, E2, and E3.…”

Overexpression of SUMO1 located predominately to euchromatin of dividing cells affects reproductive development in maize

“…These amino acid residues perform key molecular functions as they determine the efficiency (SUMO-E1 interactions), pattern (SUMO-E2 interactions) and molecular basis (SUMO-SIM interactions) of SUMO conjugation. 6 To visualize the different structural domains, we have aligned all SUMO protein sequences from Arabidopsis (AtSUMO1-8), maize (ZmSUMO1 and ZmSUMO2, the non-functional variant ZmSUMO-v and the diSUMO-like protein ZmDSUL) and human (HsSUMO1-4). Remarkably, AtSUMO1, AtSUMO2 and ZmSUMO1 contain identical amino acid residues at above described positions being involved in noncovalent interactions with E1, E2 and SIM indicating conserved functions and targets.…”