vegetative storage proteins and related proteins, similar to soybean VSPalpha and VSPbeta proteins; belongs to the haloacid dehalogenase-like superfamily
Soybean [Glycine max (L.) Merr.] vegetative storage protein VSPalpha and VSPbeta levels were identified as storage proteins due to their abundance and pattern of expression in plant tissues, they accumulate to almost one-half the amount of soluble leaf protein when soybean plants are continually depodded. They possess acid phosphatase activity which appears to be low compared to several other plant acid phosphatases; it increases in the leaves of depodded soybean plants, but to no more than 0.1% of the total acid phosphatase activity in these leaves. This acid phosphatase activity has maximal activity at pH 5.0 - 5.5, and can liberate Pi from different substrates such as napthyl acid phosphate, carboxyphenyl phosphate, sugar-phosphates, glyceraldehyde 3-phosphate, dihydroxyacetone phosphate, phosphoenolpyruvate, ATP, ADP, PPi, and short chain polyphosphates; they cleave phosphoenolpyruvate, ATP, ADP, PPI, and polyphosphates most efficiently. This family belongs to the haloacid dehalogenase-like (HAD) hydrolases, a large superfamily of diverse enzymes that catalyze carbon or phosphoryl group transfer reactions on a range of substrates, using an active site aspartate in nucleophilic catalysis. Soybean VSPalpha and VSPbeta lack this active site aspartate, other members of this family have this aspartate and may be more active. Members of this superfamily include 2-L-haloalkanoic acid dehalogenase, azetidine hydrolase, phosphonoacetaldehyde hydrolase, phosphoserine phosphatase, phosphomannomutase, P-type ATPases and many others. HAD hydrolases are found in all three kingdoms of life, and most genomes are predicted to contain multiple HAD-like proteins. Members possess a highly conserved alpha/beta core domain, and many also possess a small cap domain, the fold and function of which is variable. HAD hydrolases are sometimes referred to as belonging to the DDDD superfamily of phosphohydrolases.