Geosmin synthase

Geosmin synthase
Predicted structure of Geosmin Synthase from I-TASSER prediction
Identifiers
EC number	4.1.99.16
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Search PMC articles PubMed articles NCBI proteins

Geosmin synthase or germacradienol-geosmin synthase designates a class of bifunctional enzymes that catalyze the conversion of farnesyl diphosphate (FPP) to geosmin, a volatile organic compound known for its earthy smell. The N-terminal half of the protein catalyzes the conversion of farnesyl diphosphate to germacradienol and germacrene D, followed by the C-terminal-mediated conversion of germacradienol to geosmin. The conversion of FPP to geosmin was previously thought to involve multiple enzymes in a biosynthetic pathway.

Geosmin is found in a wide variety of microbes such as cyanobacteria and actinobacteria. Geosmin has also been found in myxobacteria, fungi, arthropods, and plants such as beets. Based on studies performed on a geosmin synthase (encoded by SCO6073) in Streptomyces coelicor and the high sequence similarity between this and other known or putative geosmin synthases (45-78% identity), it has been hypothesized that all geosmin synthases function in the same manner. Screening of available bacterial genomic data has resulted in the prediction of at least 55 putative geosmin synthases in this domain of prokaryotic organisms.

Geosmin synthase is approximately 726 amino acids in length and has two distinctive active sites on the N-terminal and C-terminal halves, respectively (in S. coelicor the N-terminal domain consists of amino acids 1-319 while the C-terminal domain exists from 374-726), both of which resembling the sesquiterpene synthase pentalenene synthase. Both the N- and C-terminal halves of the synthase contain aspartate-rich domains (DDHFLE and DDYYP, respectively) and the NSE amino acid motif (NDLFSYQRE and NDVFSYQKE, respectively), which bind trinuclear magnesium. Magnesium is a necessary cofactor, without which the synthase displays a complete lack of catalytic activity.