The flavor profile of fermented fish products is influenced by the complex interplay of microbial and enzymatic actions on the raw materials. This review summarizes the various factors contributing to the unique taste and aroma of these traditional foods. Key ingredients include locally sourced fish species and a variety of spices and seasonings that enhance flavor while serving as cultural markers. Starter cultures also play a critical role in standardizing quality and accelerating fermentation. Flavor compounds in fermented fish are primarily derived from the metabolism of carbohydrates, lipids, and proteins, producing a diverse array of free amino acids, peptides, and volatile compounds such as aldehydes, ketones, alcohols, and esters. The fermentation process can be shortened by certain methods to reduce production time and costs, allowing for faster product turnover and increased profitability in the fermented fish market. Fermented fish products also show potent beneficial effects. This review highlights the importance of integrating traditional practices with modern scientific approaches. Future research directions to enhance the quality of fermented fish products are suggested.

Single-domain antibodies, including variable domains of the heavy chains of heavy chain-only antibodies (VHHs) from camelids and variable domains of immunoglobulin new antigen receptors (VNARs) from cartilaginous fish, show the therapeutic potential of targeting antigens in a cytosol reducing environment. A large proportion of single-domain antibodies contain non-canonical cysteines and corresponding non-canonical disulfide bonds situated on the protein surface, rendering them vulnerable to environmental factors. Research on non-canonical disulfide bonds has been limited, with a focus solely on VHHs and utilizing only cysteine mutations rather than the reducing agent treatment. In this study, we examined an anti-lysozyme VNAR and an anti-BC2-tag VHH, including their non-canonical disulfide bond reduced counterparts and non-canonical cysteine mutants. Both the affinity and stability of the VNARs and VHHs decreased in the non-canonical cysteine mutants, whereas the reduced-state samples exhibited decreased thermal stability, with their affinity remaining almost unchanged regardless of the presence of reducing agents. Molecular dynamics simulations suggested that the decrease in affinity of the mutants resulted from increased flexibility of the CDRs, the disappearance of non-canonical cysteine–antigen interactions, and the perturbation of other antigen-interacting residues caused by mutations. These findings highlight the significance of non-canonical cysteines for the affinity of single-domain antibodies and demonstrate that the mutation of non-canonical cysteines is not equivalent to the disruption of non-canonical disulfide bonds with a reducing agent when assessing the function of non-canonical disulfide bonds.

Elasmobranchs are crucial for comparative studies of evolution, as they belong to the most ancient vertebrate lineages that survived numerous extinction events and persist until today. The immunoglobulin new antigen receptor (IgNAR) found in sharks and heavy-chain-only antibody (HCAb) found in camelidae are products of convergent evolution. Although it was previously believed that IgNAR emerged 220 million years ago, before the divergence of sharks and skates, there is limited evidence to support this. In this study, we provide data supporting the existence of IgNAR in the ocellate spot skate (Okamejei kenojei) mononuclear cell transcriptome and peripheral blood serum. Additionally, we characterize the germline gene configuration of the ocellate spot skate IgNAR V domain. The ocellate spot skate IgNAR structure prediction and VNAR crystal structure exhibit high similarity to their shark counterparts. These data strongly suggest that IgNAR in both sharks and skates share a common ancestor. Sequencing of the ocellate spot skate VNAR repertoire provided crucial data for further understanding of the IgNAR generation. Notably, we discovered that approximately 99% of the ocellate spot skate VNARs belonged to type IV. This represents an exceptionally high proportion of type IV within the VNAR repertoire, which has not been documented in previously studied elasmobranchs. This unique characteristic of the ocellate spot skate VNAR adds essential structural diversity to the naïve VNAR library from elasmobranchs and could potentially benefit the development of pharmaceutical drugs.

Chitin, an extracellular polysaccharide, is synthesized by membrane-embedded chitin synthase (CHS) utilizing intracellular substrates. The mechanism of the translocation of synthesized chitin across the membrane to extracellular locations remains unresolved. We prove that the chitin synthase from Phytophthora sojae (PsCHS) is a processive glycosyltransferase, which can rapidly produce and tightly bind with the highly polymerized chitin. We further demonstrate that PsCHS is a bifunctional enzyme, which is necessary and sufficient to translocate the synthesized chitin. PsCHS was purified and then reconstituted into proteoliposomes (PLs). The nascent chitin is generated and protected from chitinase degradation unless detergent solubilizes the PLs, showing that PsCHS translocates the newly produced chitin into the lumen of the PLs. We also attempted to resolve the PsCHS structure of the synthesized chitin-bound state, although it was not successful; the obtained high-resolution structure of the UDP/Mn²⁺-bound state could still assist in describing the characterization of the PsCHS’s transmembrane channel. Consistently, we demonstrate that PsCHS is indispensable and capable of translocating chitin in a process that is tightly coupled to chitin synthesis.

• Passive adsorption is bad for the structural integrity of membrane proteins. • Physiological urea level in sharks is well-tolerated by CvHAS. • 3.36 Å resolution of a VNAR-membrane protein complex structure. • Overall protocol optimization of VNAR generation against membrane proteins.