Geranylgeranyl pyrophosphate synthase; part of the gene cluster that mediates the biosynthesis of 15-deoxyoxalicine B (PubMed:30090271). The first step of the pathway is the synthesis of nicotinyl-CoA from nicotinic acid by the nicotinic acid-CoA ligase olcI (PubMed:30090271). Nicotinyl-CoA is then a substrate of polyketide synthase olcA to produce 4-hydroxy-6-(3-pyridinyl)-2H-pyran-2-one (HPPO) which is further prenylated by the polyprenyl transferase olcH to yield geranylgeranyl-HPPO (PubMed:30090271). Geranylgeranyl pyrophosphate is provided by the cluster-specific geranylgeranyl pyrophosphate synthase olcC (PubMed:30090271). The FAD-dependent monooxygenase olcE catalyzes the epoxidation of geranylgeranyl-HPPO and the terpene cyclase olcD catalyzes the cyclization of the terpenoid component, resulting in the formation of the tricyclic terpene moiety seen in predecaturin E (PubMed:30090271). The cytochrome P450 monooxygenase then catalyzes the allylic oxidation of predecaturin E, which is followed by spirocylization with concomitant loss of one molecule of water to form decaturin E (PubMed:30090271). Decaturin E is the substrate of the cytochrome P450 monooxygenase olcJ which hydroxylates it at the C-29 position to form decaturin F (PubMed:30090271). The short-chain dehydrogenase/reductase olcF may catalyze the oxidation of decaturin F to generate the 29-hydroxyl-27-one intermediate, and subsequent hemiacetal formation probably leads to the formation of decaturin C (Probable). The dioxygenase olcK may be a peroxisomal enzyme that catalyzes the hydroxylation of decaturin C into decaturin A once decaturin C is shuttled into the peroxisome by the MFS transporter olcL (Probable). Finally the cytochrome P450 monooxygenase olcB catalyzes the oxidative rearrangement to yield 15-deoxyoxalicine B (PubMed:30090271). In the absence of olcJ, decaturin E may be shunted to a pathway in which it is oxidized to a ketone, possibly by olcF, to form decaturin D, which undergoes further allylic oxidation to yield decaturin G (PubMed:30090271). Moreover, in the absence of oclK or oclL, oclB can convert decaturin C into 15-deoxyoxalicine A (PubMed:30090271). dimethylallyl diphosphate + isopentenyl diphosphate = (2E)-geranyl diphosphate + diphosphate (2E)-geranyl diphosphate + isopentenyl diphosphate = (2E,6E)-farnesyl diphosphate + diphosphate (2E,6E)-farnesyl diphosphate + isopentenyl diphosphate = (2E,6E,10E)-geranylgeranyl diphosphate + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Strongly decreases the production of 15-deoxyoxalicine B. The 15-deoxyoxalicine B cluster is a rare cluster that contains its own geranylgeranyl pyrophosphate synthase (olcC), in contrast to other related clusters which rely on a FPP/GGPP synthase localized outside of the cluster. Belongs to the FPP/GGPP synthase family.