Fucosylation and galactosylation in N-glycans of bovine intestinal alkaline phosphatase and their role in its enzymatic activity.

Bovine intestinal alkaline phosphatase (biALP), a membrane-bound plasma metalloenzyme, maintains intestinal homeostasis, regulates duodenal surface pH, and protects against infections caused by pathogenic bacteria. The N-glycans of biALP regulate its enzymatic activity, protein folding, and thermostability, but their structures are not fully reported. In this study, the structures and quantities of the N-glycans of biALP were analyzed by liquid chromatography-electrospray ionization-high energy collision dissociation-tandem mass spectrometry. In total, 48 N-glycans were identified and quantified, comprising high-mannose [6 N-glycans, 33.1 % (sum of relative quantities of each N-glycan)], hybrid (6, 11.9 %), and complex (36, 55.0 %) structures [bi- (13, 26.1 %), tri- (16, 21.5 %), and tetra-antennary (7, 7.4 %)]. These included bisecting N-acetylglucosamine (33, 56.6 %), mono-to tri-fucosylation (32, 53.3 %), mono-to tri-α-galactosylation (16, 20.7 %), and mono-to tetra-ß-galactosylation (36, 58.5 %). No sialylation was identified. N-glycans with non-bisecting GlcNAc (9, 10.3 %), non-fucosylation (10, 13.6 %), non-α-galactosylation (26, 46.2 %), and non-ß-galactosylation (6, 8.4 %) were also identified. The activity (100 %) of biALP was reduced to 37.3 ± 0.2 % (by de-fucosylation), 32.7 ± 2.9 % (by de-α-galactosylation), and 0.2 ± 0.2 % (by de-ß-galactosylation), comparable to inhibition by 10-4 to 101 mM EDTA, a biALP inhibitor. These results indicate that fucosylated and galactosylated N-glycans, especially ß-galactosylation, affected the activity of biALP. This study is the first to identify 48 diverse N-glycan structures and quantities of bovine as well as human intestinal ALP and to demonstrate the importance of the role of fucosylation and galactosylation for maintaining the activity of biALP.

Protective effects of Capsicum fruits and their constituents on damage in TNF-α-stimulated human dermal fibroblasts.

BACKGROUND: Antioxidant and anti-inflammatory effects of natural products on skin cells have been proved to be effective in improving skin damage. Capsicum species contain capsaicinoids that have antioxidant and anti-inflammatory properties, and various subspecies are cultivated. In this study, the effects of four Capsicum fruits and major constituents on oxidative stress and inflammatory reactions were measured using human dermal fibroblasts (HDFs) to verify their effects on skin damage. RESULTS: The inhibitory effects of nitric oxide (NO), reactive oxygen species (ROS), and prostaglandin E2 (PGE2 ) by cucumber hot pepper, red pepper (RDP), Shishito pepper (SSP), and Cheongyang pepper were determined in HDFs. RDP and SSP inhibited the production of NO, ROS, and PGE2 in tumor necrosis factor-alpha-stimulated HDFs. Additionally, SSP seeds restored tumor necrosis factor-alpha-induced increase in matrix metalloproteinase-1 and decreased procollagen I α1 (COLIA1). In high-performance liquid chromatography analysis of the capsaicinoids capsaicin (CAP) and dihydrocapsaicin (DHC), CAP was detected at a higher level than DHC in the peel and seeds of all four types of Capsicum fruits, and the total amount of capsaicinoids was the highest in SSP. CAP and DHC, which are major constituents of Capsicum fruits, also inhibited NO, ROS, and PGE2 and restored matrix metalloproteinase-1 and procollagen I α1. CONCLUSION: RDP and SSP were shown to have a significant protective effect on skin damage, including oxidative stress, inflammatory reactions, and reduction of collagens. Capsaicinoids CAP and DHC were proved as active constituents. This research may provide basic data for developing Capsicum fruits as ingredients to improve skin damage, such as inflammation and skin aging. © 2022 Society of Chemical Industry.

Structural identification and quantification of unreported sialylated N-glycans in bovine testicular hyaluronidase by LC-ESI-HCD-MS/MS.

Bovine testicular hyaluronidase (BTH), which accelerates the absorption and dispersion of drugs by decomposing hyaluronan in subcutaneous tissues, has been used in medical applications, including local anesthesia, ophthalmology, and dermatosurgery. The requirement of N-glycans for the activity of human hyaluronidase has been reported, and BTH has greater activity than human hyaluronidase. However, the N-glycan characteristics of BTH are unclear. From a commercial BTH source containing additional proteins, purified BTH (pBTH) was obtained using size exclusion chromatography, and the structures and quantities of its N-glycans were analyzed using liquid chromatography (LC)-electrospray ionization-higher energy collisional dissociation (HCD)-tandem mass spectrometry (MS/MS). In pBTH, 32 N-glycans were identified, with 12 sialylations (39.0% of total N-glycan content), nine core-fucosylations (31.5%), six terminal galactosylations (14.6%), five high-mannosylations (13.7%), and four bisecting N-acetylglucosamine structures (7.8%). The presence of sialylated glycopeptides in pBTH was confirmed by nano-LC-HCD-MS/MS analysis. The absolute quantity of all N-glycans was calculated as 1.4 pmol (0.6 pmol for sialylation) in pBTH (1.0 pmol). The sialylation level (related to half-life, thermal stability, resistance to proteolysis, and solubility) was 24.4 times higher than that of human hyaluronidase. The hyaluronan degradation activity of de-sialylated pBTH decreased to 41.2 ± 4.2%, showing that sialylated N-glycans were required for pBTH activity as well. This is the first study to identify and quantify 32 N-glycans of pBTH and investigate their structural roles in its activity. The presence of larger amounts of sialylated N-glycans in pBTH than in human hyaluronidase suggests a greater utilization of pBTH.

Comparison of sialylated and fucosylated N-glycans attached to Asn 6 and Asn 41 with different roles in hyaluronan and proteoglycan link protein 1 (HAPLN1).

Hyaluronan and proteoglycan link protein 1 (HAPLN1) is an extracellular matrix protein stabilizing interactions between hyaluronan and proteoglycan. Although HAPLN1 is being investigated for various biological roles, its N-glycosylation is poorly understood. In this study, the structure of N-glycopeptides of trypsin-treated recombinant human HAPLN1 (rhHAPLN1) expressed from CHO cells were identified by nano-liquid chromatography-tandem mass spectrometry. A total of 66 N-glycopeptides were obtained, including 16 and 12 N-glycans at sites Asn 6 (located in the N-terminal region) and Asn 41 (located in the Ig-like domain, which interacts with proteoglycan), respectively. The quantities (%) of each N-glycan relative to the totals (100 %) at each site were calculated. Tri- and tetra-sialylation (to resist proteolysis and extend half-life) were more abundant at Asn 6, and di- (core- and terminal-) fucosylation (to increase binding affinity and stability) and sialyl-Lewis X/a epitope (a major ligand for E-selectin) were more abundant at Asn 41. These results indicate that N-glycans attached to Asn 6 (protecting HAPLN1) and Asn 41 (supporting molecular interactions) play different roles in HAPLN1. This is the first study of site-specific N-glycosylation in rhHAPLN1, which will be useful for understanding its molecular interactions in the extracellular matrix.

Identification, quantification, and structural role of N-glycans in two highly purified isoforms of sheep testicular hyaluronidase.

Animal-derived hyaluronidase, which hydrolyzes the polysaccharide hyaluronic acid, has been used in medical applications despite its limited purity. Additionally, the N-glycan characterization of sheep testicular hyaluronidase (STH) and its structural role remain poorly understood. In this study, STH was purified from the commercially available STH preparation (containing at least 14 impurity proteins) using heparin-affinity chromatography followed by size exclusion chromatography. The structure and quantity of N-glycans of STH were investigated using liquid chromatography-electrospray ionization-high energy collision dissociation-tandem mass spectrometry. Two isoforms, H3S1 and H3S2, of STH were obtained (purity >98 %) with a yield of 3.4 % and 5.1 %, respectively. Fourteen N-glycans, including nine core-fucosylated N-glycans (important for the stability and function of glycoproteins), were identified in both H3S1 and H3S2, with similar quantities of each N-glycan. The amino acid sequences of the proteolytic peptides of H3S1 and H3S2 were compared with those reported in STH. The hyaluronic acid-degrading activity of deglycosylated H3S1 and H3S2 was reduced to 70.8 % and 71.1 % compared to that (100 %) of H3S1 and H3S2, respectively. This is the first report of N-glycan characterization of two highly purified isoforms of STH. These H3S1 and H3S2 will be useful for medical use without unwanted effects of partially purified STH.

Fragmentation stability and retention time-shift obtained by LC-MS/MS to distinguish sialylated N-glycan linkage isomers in therapeutic glycoproteins.

Sialylated N-glycan isomers with α2-3 or α2-6 linkage(s) have distinctive roles in glycoproteins, but are difficult to distinguish. Wild-type (WT) and glycoengineered (mutant) therapeutic glycoproteins, cytotoxic T lymphocyte-associated antigen-4-immunoglobulin (CTLA4-Ig), were produced in Chinese hamster ovary cell lines; however, their linkage isomers have not been reported. In this study, N-glycans of CTLA4-Igs were released, labeled with procainamide, and analyzed by liquid chromatography-tandem mass spectrometry (MS/MS) to identify and quantify sialylated N-glycan linkage isomers. The linkage isomers were distinguished by comparison of 1) intensity of the N-acetylglucosamine ion to the sialic acid ion (Ln/Nn) using different fragmentation stability in MS/MS spectra and 2) retention time-shift for a selective m/z value in the extracted ion chromatogram. Each isomer was distinctively identified, and each quantity (>0.1%) was obtained relative to the total N-glycans (100%) for all observed ionization states. Twenty sialylated N-glycan isomers with only α2-3 linkage(s) in WT were identified, and each isomer's sum of quantities was 50.4%. Furthermore, 39 sialylated N-glycan isomers (58.8%) in mono- (3 N-glycans; 0.9%), bi- (18; 48.3%), tri- (14; 8.9%), and tetra- (4; 0.7%) antennary structures of mutant were obtained, which comprised mono- (15 N-glycans; 25.4%), di- (15; 28.4%), tri- (8; 4.8%), and tetra- (1; 0.2%) sialylation, respectively, with only α2-3 (10 N-glycans; 4.8%), both α2-3 and α2-6 (14; 18.4%), and only α2-6 (15; 35.6%) linkage(s). These results are consistent with those for α2-3 neuraminidase-treated N-glycans. This study generated a novel plot of Ln/Nn versus retention time to distinguish sialylated N-glycan linkage isomers in glycoprotein.

Peptide-N-glycosidase F or A treatment and procainamide-labeling for identification and quantification of N-glycans in two types of mammalian glycoproteins using UPLC and LC-MS/MS.

BACKGROUND: N-glycans in glycoproteins can affect physicochemical properties of proteins; however, some reported N-glycan structures are inconsistent depending on the type of glycoprotein or the preparation methods. OBJECTIVE: To obtain consistent results for qualitative and quantitative analyses of N-glycans, N-glycans obtained by different preparation methods were compared for two types of mammalian glycoproteins. METHODS: N-glycans are released by peptide-N-glycosidase F (PF) or A (PA) from two model mammalian glycoproteins, bovine fetuin (with three glycosylation sites) and human IgG (with a single glycosylation site), and labeled with a fluorescent tag [2-aminobenzamide (AB) or procainamide (ProA)]. The structure and quantity of each N-glycan were determined using UPLC and LC-MS/MS. RESULTS: The 21 N-glycans in fetuin and another 21 N-glycans in IgG by either PF-ProA or PA-ProA were identified using LC-MS/MS. The N-glycans in fetuin (8-13 N-glycans were previously reported) and in IgG (19 N-glycans were previously reported), which could not be identified by using the widely used PF-AB, were all identified by using PF-ProA or PA-ProA. The quantities (%) of the N-glycans (>0.1 %) relative to the total amount of N-glycans (100 %) obtained by AB- and ProA-labeling using LC-MS/MS had a similar tendency. However, the absolute quantities (pmol) of the N-glycans estimated using UPLC and LC-MS/MS were more efficiently determined with ProA-labeling than with AB-labeling. Thus, PF-ProA or PA-ProA allows for more effective identification and quantification of N-glycans than PF-AB in glycoprotein, particularly bovine fetuin. This study is the first comparative analysis for the identification and relative and absolute quantification of N-glycans in glycoproteins with PF-ProA and PA-ProA using UPLC and LC-MS/MS.