Polysialic acid (polySia) is an unusual glycan that posttranslational modifies neural cell adhesion molecule (NCAM) proteins in mammalian cells. The up-regulated expression of polySia-NCAM is associated with tumor progression in many metastatic human cancers and in neurocognitive processes. Two members of the ST8Sia family of α2,8-polysialyltransferases (polySTs), ST8Sia II (STX) and ST8Sia IV (PST) both catalyze synthesis of polySia when activated cytidine monophosphate(CMP)-Sialic acid (CMP-Sia) is translocate into the lumen of the Golgi apparatus. Two key polybasic domains in the polySTs, the polybasic region (PBR) and the polysialyltransferase domain (PSTD) areessential forpolysialylation of the NCAM proteins. However, the precise molecular details to describe the interactions required for polysialylation remain unknown. In this study, we hypothesize that PSTD interacts with both CMP-Sia and polySia to catalyze polysialylation of the NCAM proteins. To test this hypothesis, we synthesized a 35-amino acid-PSTD peptide derived from the ST8Sia IV gene sequence and used it to study its interaction with CMP-Sia, and polySia. Our results showed for the PSTD-CMP-Sia interaction, the largest chemical-shift perturbations (CSP) were in amino acid residues V251 to A254 in the short H1 helix, located near the N-terminus of PSTD. However, larger CSP values for the PSTD-polySia interaction were observed in amino acid residues R259 to T270 in the long H2 helix. These differences suggest that CMP-Sia preferentially binds to the domain between the short H1 helix and the longer H2 helix. In contrast, polySia was principally bound to the long H2 helix of PSTD. For the PSTD-polySia interaction, a significant decrease in peak intensity was observed in the 20 amino acid residues located between the N-and C-termini of the long H2 helix in PSTD, suggesting a slower motion in these residues when polySia bound to PSTD. Specific features of the interactions between PSTD-CMP-Sia, and PSTD-polySia were further confirmed by comparing their 800 MHz-derived HSQC spectra with that of PSTD-Sia, PSTD-TriSia (DP 3) and PSTD-polySia. Based on the interactions between PSTD-CMP-Sia, PSTD-polySia, PBR-NCAM and PSTD-PBR, these findingsprovide a greater understanding of the molecular mechanisms underlying polySia-NCAM polysialylation, and thus provides a new perspective for translational pharmacological applications and development by targeting the two polysialyltransferases.

The expression of polysialic acid (polySia) on the neuronal cell adhesion molecule (NCAM) is called NCAM-polysialylation, which is strongly related to the migration and invasion of tumor cells and aggressive clinical status. During the NCAM polysialylation process, polysialyltransferases (polySTs), such as polysialyltransferase IV (ST8SIA4) or polysialyltransferase II (ST8SIA2), can catalyze the addition of CMP-sialic acid (CMP-Sia) to the NCAM to form polysialic acid (polySia). In this study, the docking models of polysialyltransferase IV (ST8Sia4) protein and different ligands were predicted using Alphafold 3 and DiffDock servers, and the prediction accuracy was further verified using the NMR experimental spectra of the interactions between polysialyltransferase domain (PSTD), a crucial peptide domain in ST8Sia4, and a different ligand. This combination strategy provides new insights into a quick and effective screening for inhibitors of tumor cell migration.

It is known that sialyllactose (SL) in mammalians is a major source of sialic acid (Sia), which can further form cytidine monophosphate sialic acid (CMP-Sia), and the final product is polysialic acid (polySia) using polysialyltransferases (polySTs) on the neural cell adhesion molecule (NCAM). This process is called NCAM polysialylation. The overexpression of polysialylation is strongly related to cancer cell migration, invasion, and metastasis. In order to inhibit the overexpression of polysialylation, in this study, SL was selected as an inhibitor to test whether polysialylation could be inhibited. Our results suggest that the interactions between the polysialyltransferase domain (PSTD) in polyST and CMP-Siaand the PSTD and polySia could be inhibited when the 3′-sialyllactose (3′-SL) or 6′-sialyllactose (6′-SL) concentration is about 0.5 mM or 6′-SL and 3 mM, respectively. The results also show that SLs (particularly for 3′-SL) are the ideal inhibitors compared with another two inhibitors, low-molecular-weight heparin (LMWH) and cytidine monophosphate (CMP), because 3’-SL can not only be used to inhibit NCAM polysialylation, but is also one of the best supplements for infant formula and the gut health system.

Advanced bladder cancer (BCa) is associated with a poor prognosis, highlighting the urgent need for novel therapeutic strategies with improved efficacy and reduced toxicity. Nectin-4 (PVRL4, here after referred to as N4) is a clinically validated therapeutic target; however, existing antibody-based agents are limited by inadequate tumor penetration and off-target toxicities. Nanobodies (Nbs) possess favorable characteristics, including small molecular size, enhanced tissue penetration, and ease of sengineering. This study aimed to identify and preliminarily characterize N4-targeting Nb candidates for BCa using a yeast surface display-based screening strategy. N4 was highly expressed in BCa and significantly associated with an unfavorable prognosis. The YSD platform supported efficient library expansion, surface display, and iterative enrichment of N4-binding clones. Among the identified Nbs, Nb-80 exhibited apparent binding activity, with an EC₅₀ of 0.150 μg/mL. BLI analysis demonstrated rapid association-dissociation kinetics. An N4-binding Nb candidate was identified and preliminarily characterized using a YSD-based screening strategy. These findings support the utility of the YSD platform for Nb discovery and provide a preliminary basis for further validation of N4-targeting Nb candidates in BCa. Not applicable.

Chitin is the second most abundant natural renewable biomass, widely present in seafood waste. Nevertheless, its crystalline structure makes processing difficult. Ectoine, a high value compatible solute, is common in pharmaceuticals and cosmetics. However, direct ectoine production from chitinous waste using wild-type microbial strains is rarely reported. Here, we show that Vibrio diabolicus X511 possesses a complete ectoine biosynthetic gene cluster (ectABC-ask) as well as native chitinolytic genes. These genomic features are consistent with the strain’s ability to directly ferment colloidal chitin, crab shell flakes, and shrimp shell powder for ectoine production, eliminating the need for exogenous chitinase supplementation. With 5 g/L yeast extract as the nitrogen source, strain X511 produced 2.172 g/L ectoine from colloidal chitin, a titer comparable to, or even higher than, those reported for several wild-type strains grown on soluble carbon sources. Using highly crystalline crab shell flakes and raw shrimp shell powder as substrates, the strain achieved titers of 0.259 g/L and 0.181 g/L respectively, accompanied by substrate weight losses of 60% and 43.47%. FESEM, XRD, and FTIR analyses confirmed the strain’s capacity to effectively disrupt crystalline structure of chitin and degrade raw shrimp shell biomass. These findings suggest that X511 may be a promising biocatalyst for the effective bioconversion of chitinous waste to high value chemicals.