Terpene cyclases (TCs), extraordinary enzymes that create the structural diversity seen in terpene natural products, are traditionally divided into two classes, class I and class II. Although the structural and mechanistic features of class I TCs are well-known, the corresponding details in class II counterparts have not been fully characterized. Here, we report the genome mining discovery and structural characterization of two class II sesquiterpene cyclases (STCs) from Streptomyces. These drimenyl diphosphate synthases (DMSs) are the first STCs shown to possess β,γ-didomain architecture. High-resolution X-ray crystal structures of DMS from Streptomyces showdoensis (SsDMS) in complex with both a farnesyl diphosphate and Mg2+ unveiled an induced-fit mechanism, with an unprecedented Mg2+ binding mode, finally solving one of the lingering questions in class II TC enzymology. This study supports continued genome mining for novel bacterial TCs and provides new mechanistic insights into canonical class II TCs that will lead to advances in TC engineering and synthetic biology.

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Background and Purpose: Although no effective therapy is available to stop or reverse CKD progression targeting its key feature, the loss of peritubular capillaries (PTCs) leading to interstitial fibrosis, myeloid-derived growth factor (MYDGF) with tissue-repairing activities enlightens its therapeutic potential for CKD. However, the extremely short circulatory lifetime (15 min) restricts its application.Experimental Approach: We selected a tandem repeated (TR) region of human CD164 as a carrier to fuse with MYDGF and then investigated for biophysical and pharmacokinetic changes. The MYDGF164 bioactivities were validated in HUVECs and then assessed in HK-2 cells. We also investigated its efficacy in unilateral ureteral obstruction (UUO)-treated mice and in adenine-induced CKD rats.Key results: MYDGF164 was modified with sialoglycans, improving its resistance to serum proteases and increasing its hydrodynamic radius. The half-life of MYDGF164 was significantly prolonged but retained its original cell proliferation, anti-apoptosis, and tubulogenesis activities. It selectively stimulated the proliferation in endothelial and epithelial cells through phosphorylating MAPK1/3. MYDGF164 alleviated capillary rarefaction, hypoxia, renal fibrosis, and tubular atrophy in UUO mice and in adenine-induced CKD rats. MYDGF164 restored renal function, with normalized creatinine and urea levels in adenine-induced CKD rats. Histopathology and immunohistochemistry revealed that MYDGF164 protection was related to its cell-proliferative, anti-apoptosis, and angiogenesis activities. Conclusions and Implications:This study is the first successful example of using a tandem repeated region of hCD164 as a cargo protein for the pharmacokinetic improvement of therapeutic proteins. Our findings highlight the potential of MYDGF164 in alleviating renal fibrosis in CKD.

Terpene cyclases (TCs), the extraordinary enzymes that create the structural diversity seen in terpene natural products, are traditionally divided into two classes. Although the structural and mechanistic features in class I TCs are well-known, the corresponding details in class II counterparts have not been fully characterized. Here, we report the genome mining discovery and structural characterization of two class II sesquiterpene cyclases (STCs) from Streptomyces. These drimenyl diphosphate synthases (DMSs) are the first STCs shown to possess β,γ-didomain architecture. High-resolution X-ray crystal structures of SsDMS in complex with both a farnesyl diphosphate and Mg2+ unveiled an induced-fit mechanism with an unprecedented Mg2+ binding mode, finally solving one of the lingering questions in class II TC enzymology. This study supports continued genome mining for novel bacterial TCs and provides new mechanistic insights into canonical class II TCs that will lead to advances in TC engineering and synthetic biology.

Mannose 2-epimerase (ME), a member of the acylglucosamine 2-epimerase (AGE) superfamily that catalyzes epimerization of D-mannose and D-glucose, has recently been characterized to have potential for D-mannose production. However, the substrate-recognition and catalytic mechanism of ME remains unknown. In this study, structures of Runella slithyformis ME (RsME) and its D254A mutant [RsME(D254A)] were determined in their apo forms and as intermediate-analog complexes [RsME–D-glucitol and RsME(D254A)–D-glucitol]. RsME possesses the (α/α)6-barrel of the AGE superfamily members but has a unique pocket-covering long loop (loopα7–α8). The RsME–D-glucitol structure showed that loopα7–α8 moves towards D-glucitol and closes the active pocket. Trp251 and Asp254 in loopα7–α8 are only conserved in MEs and interact with D-glucitol. Kinetic analyses of the mutants confirmed the importance of these residues for RsME activity. Moreover, the structures of RsME(D254A) and RsME(D254A)–D-glucitol revealed that Asp254 is vital for binding the ligand in a correct conformation and for active-pocket closure. Docking calculations and structural comparison with other 2-epimerases show that the longer loopα7–α8 in RsME causes steric hindrance upon binding to disaccharides. A detailed substrate-recognition and catalytic mechanism for monosaccharide-specific epimerization in RsME has been proposed.