InterPro domain: IPR034087

This entry represents a group of invertase inhibitors, known as cell wall/vacuolar inhibitor of fructosidase (C/VIF1) from plants.

Cell-wall invertases (CWIs) are secreted apoplastic enzymes belonging to the glycoside hydrolase family 32 ( 3.2.1.26 ) that catalyze the hydrolytic cleavage of the disaccharide sucrose into glucose and fructose. Their activity is tightly regulated by compartment-specific inhibitor proteins at transcriptional and post-transcriptional levels [ 1 ].

Invertase inhibitors are structurally similar to those of pectin methylesterase (PMEIs), an enzyme that is involved in the control of pectin metabolism and is structurally unrelated to invertases. All inhibitors share a size of about 18kDa, two strictly conserved disulfide bridges and only moderate sequence homology (about 20% sequence identity). Interaction of invertase inhibitor Nt-CIF (Nicotiana tabacum cell-wall inhibitor of beta-fructosidase) with CWI is strictly pH-dependent, modulated between pH 4 and 6, with rapid dissociation at neutral pH mediated by structure rearrangement or surface charge pattern in the binding interface [ 2 ]. Comparison of the CIF/INV1 structure with the complex between the structurally CIF-related pectin methylesterase inhibitor (PMEI) and pectin methylesterase indicates a common targeting mechanism in PMEI and CIF [ 3 ].

1. Plant protein inhibitors of invertases. Biochim. Biophys. Acta 1696, 253-61
2. Multiple crystal forms of the cell-wall invertase inhibitor from tobacco support high conformational rigidity over a broad pH range. Acta Crystallogr. D Biol. Crystallogr. 62, 665-70
3. Structural insights into the pH-controlled targeting of plant cell-wall invertase by a specific inhibitor protein. Proc. Natl. Acad. Sci. U.S.A. 107, 17427-32