As the first catalyzing enzyme in the MVA pathway, HMGS plays an important role in the biosynthesis of terpenoids in plants (Rodriguez- Concepcion and Boronat, 2002).
(2014) summarized the past investigations on eukaryotic HMGS with particular focus on advance of plant HMGS study by researchers in China.
Biological significance of plant HMGS in the MVA pathway: As an important condensing enzyme in the MVA pathway, HMGS can catalyze condensation of acetyl-CoA and acetoacetyl-CoA to generate HMG-CoA, which is further converted into generate MVA by HMGR.
HMGS can be classified broadly into cytosolic and mitochondrial forms (Clinkenbeard et al., 1975a, 1975b).
Structure of plant HMGS protein: The plant HMGS protein is generally composed of 460-500 amino acid residues and has a relative molecular mass of 50-60 kDa (Argout et al., 2008; Schnable et al., 2009; Schilmiller et al., 2009; Zhang et al., 2011; Kai et al., 2013).
Previous results have revealed that plant HMGS proteins are highly similar in their 3-D structures, which consist of two structural regions referred to as the upper and lower regions, similar to the HMGS from Staphylococcus aureus (Figure 2; Campobasso et al., 2004).
Most HMGS proteins contain a conserved motif 'NxD/NE/VEGI/VDx(2)NACF/YxG', which is considered to be important for HMGS function (Figure 3).
Cys117, His247 and Glu83 in BjHMGS1form a catalytic group common in HMGS to finish the three-stepreaction to produce HMG-CoA.
Regulatory mechanism of HMGS in plants: HMGS participates in the synthesis of precursors of isoprenoids and provides reactive substrates for HMGR.
The results mentioned above implied that HMGS in higher plants might be is also under synergistic feedback regulation by several secondary metabolites such as isoprenoids.