Glycan-shielded homodimer structure and dynamical features of the canine distemper virus hemagglutinin relevant for viral entry and efficient vaccination.

Canine distemper virus (CDV) belongs to morbillivirus, including measles virus (MeV) and rinderpest virus, which causes serious immunological and neurological disorders in carnivores, including dogs and rhesus monkeys, as recently reported, but their vaccines are highly effective. The attachment glycoprotein hemagglutinin (CDV-H) at the CDV surface utilizes signaling lymphocyte activation molecule (SLAM) and Nectin-4 (also called poliovirus-receptor-like-4; PVRL4) as entry receptors. Although fusion models have been proposed, the molecular mechanism of morbillivirus fusion entry is poorly understood.

Impact of Micropolymorphism Outside the Peptide Binding Groove in the Clinically Relevant Allele HLA-C*14 on T Cell Responses in HIV-1 Infection.

There is increasing evidence for the importance of human leukocyte antigen C (HLA-C)-restricted CD8 T cells in HIV-1 control, but these responses are relatively poorly investigated. The number of HLA-C-restricted HIV-1 epitopes identified is much smaller than those of HLA-A-restricted or HLA-B-restricted ones. Here, we utilized a mass spectrometry-based approach to identify HIV-1 peptides presented by HLA-C*14:03 protective and HLA-C*14:02 nonprotective alleles.

Low-Cost Cell-Surface-Mimic Analysis of Ligand Interactions of Biotinylated Immune Receptors Using Surface Plasmon Resonance.

On the immune cell surface, many immune receptors are expressed and modulate the inhibitory or activating signals to control the immune responses. Recently, some of these receptors have been categorized as immune checkpoint receptors and targeted for cancer immunity or autoimmune diseases. To analyze the weak and fast binding typical for immune receptor-ligand interactions, a real-time surface plasmon resonance (SPR) technique is useful.

Ca Regulates ERp57-Calnexin Complex Formation.

ERp57, a member of the protein disulfide isomerase family, is a ubiquitous disulfide catalyst that functions in the oxidative folding of various clients in the mammalian endoplasmic reticulum (ER). In concert with ER lectin-like chaperones calnexin and calreticulin (CNX/CRT), ERp57 functions in virtually all folding stages from co-translation to post-translation, and thus plays a critical role in maintaining protein homeostasis, with direct implication for pathology. Here, we present mechanisms by which Ca regulates the formation of the ERp57-calnexin complex.

Efficient preparation of human and mouse CD1d proteins using silkworm baculovirus expression system.

CD1d is a major histocompatibility complex (MHC) class I-like glycoprotein and binds to glycolipid antigens that are recognized by natural killer T (NKT) cells. To date, our understanding of the structural basis for glycolipid binding and receptor recognition of CD1d is still limited. Here, we established a preparation method for the ectodomain of human and mouse CD1d using a silkworm-baculovirus expression system.

Structure of HIV-2 Nef Reveals Features Distinct from HIV-1 Involved in Immune Regulation.

The human immunodeficiency virus (HIV) accessory protein Nef plays a major role in establishing and maintaining infection, particularly through immune evasion. Many HIV-2-infected people experience long-term viral control and survival, resembling HIV-1 elite control. HIV-2 Nef has overlapping but also distinct functions from HIV-1 Nef.

Evaluation of the Reactivity and Receptor Competition of HLA-G Isoforms toward Available Antibodies: Implications of Structural Characteristics of HLA-G Isoforms.

The human leucocyte antigen (HLA)-G, which consists of seven splice variants, is a tolerogenic immune checkpoint molecule. It plays an important role in the protection of the fetus from the maternal immune response by binding to inhibitory receptors, including leukocyte Ig-like receptors (LILRs). Recent studies have also revealed that HLA-G is involved in the progression of cancer cells and the protection from autoimmune diseases.

Therapeutic effects of soluble human leukocyte antigen G2 isoform in lupus-prone MRL/lpr mice.

Human leukocyte antigen (HLA)-G, a non-classical HLA class I molecule, has one of the splicing isoforms, HLA-G2, which lacks one domain (α2) and forms a non-covalent homodimer. HLA-G2 is expressed on placental cells, regulatory T cells, tumor cells, and virus-infected cells, and is involved in immunosuppression. The major isoform of HLA-G, HLA-G1, binds to leukocyte immunoglobulin (Ig)-like receptor (LILR) B1 and LILRB2, on the contrary, HLA-G2 binds to only LILRB2.

Structural and Functional Basis for LILRB Immune Checkpoint Receptor Recognition of HLA-G Isoforms.

Human leukocyte Ig-like receptors (LILR) LILRB1 and LILRB2 are immune checkpoint receptors that regulate a wide range of physiological responses by binding to diverse ligands, including HLA-G. HLA-G is exclusively expressed in the placenta, some immunoregulatory cells, and tumors and has several unique isoforms. However, the recognition of HLA-G isoforms by LILRs is poorly understood.

Specificity of Morbillivirus Hemagglutinins to Recognize SLAM of Different Species.

Measles virus (MV) and canine distemper virus (CDV) are highly contagious and deadly, forming part of the morbillivirus genus. The receptor recognition by morbillivirus hemagglutinin (H) is important for determining tissue tropism and host range. Recent reports largely urge caution as regards to the potential expansion of host specificities of morbilliviruses.

Crystal structure of the complex between venom toxin and serum inhibitor from Viperidae snake.

Venomous snakes have endogenous proteins that neutralize the toxicity of their venom components. We previously identified five small serum proteins (SSP-1-SSP-5) from a highly venomous snake belonging to the family Viperidae as inhibitors of various toxins from snake venom. The endogenous inhibitors belong to the prostate secretory protein of 94 amino acids (PSP94) family.

Structural and thermodynamic analyses reveal critical features of glycopeptide recognition by the human PILRα immune cell receptor.

Before entering host cells, herpes simplex virus-1 uses its envelope glycoprotein B to bind paired immunoglobulin-like type 2 receptor α (PILRα) on immune cells. PILRα belongs to the Siglec (sialic acid (SA)-binding immunoglobulin-like lectin)-like family, members of which bind SA. PILRα is the only Siglec member to recognize not only the sialylated -linked sugar T antigen (sTn) but also its attached peptide region.

Therapeutic application of human leukocyte antigen-G1 improves atopic dermatitis-like skin lesions in mice.

Human leukocyte antigen (HLA)-G is an immune checkpoint molecule that plays critical roles in immune response and in triggering inhibitory signaling to immune cells such as T cells, natural killer cells, and antigen-presenting cells. Thus, the application of HLA-G can be considered for treating immune response-related inflammatory disorders. We have previously reported that treatment with HLA-G1 and HLA-G2 ameliorates the joint swelling associated with collagen-induced arthritis of DBA/1 mice, an animal model for rheumatoid arthritis.

Cutting Edge: Class II-like Structural Features and Strong Receptor Binding of the Nonclassical HLA-G2 Isoform Homodimer.

HLA-G is a natural tolerogenic molecule and has the following unique features: seven isoforms (HLA-G1 to HLA-G7), formation of disulfide-linked homodimers, and β2-microglobulin (β2m)-free forms. Interestingly, individuals null for the major isoform, HLA-G1, are healthy and expressed the α2 domain-deleted isoform, HLA-G2, which presumably compensates for HLA-G1 function. However, the molecular characteristics of HLA-G2 are largely unknown.

HIV-1 Control by NK Cells via Reduced Interaction between KIR2DL2 and HLA-C12:02/C14:03.

Natural killer (NK) cells control viral infection in part through the interaction between killer cell immunoglobulin-like receptors (KIRs) and their human leukocyte antigen (HLA) ligands. We investigated 504 anti-retroviral (ART)-free Japanese patients chronically infected with HIV-1 and identified two KIR/HLA combinations, KIR2DL2/HLA-C12:02 and KIR2DL2/HLA-C14:03, that impact suppression of HIV-1 replication. KIR2DL2 NK cells suppressed viral replication in HLA-C14:03 or HLA-C12:02 cells to a significantly greater extent than did KIR2DL2 NK cells in vitro.

Rapid Screening by Cell-Based Fusion Assay for Identifying Novel Antivirals of Glycoprotein B-Mediated Herpes Simplex Virus Type 1 Infection.

Herpes simplex virus type 1 (HSV-1) is a causative agent for a variety of diseases. Although antiherpetic drugs such as acyclovir have been developed to inhibit virus replication through interaction with DNA kinases, their continuous administration leads to an increase in the frequency of drug-resistant HSV-1, which is an important clinical issue that requires urgent solution. Recently, we reported that the sialylated O-linked sugar T antigen (sTn) and its attached peptide region (O-glycosylated sTn peptide) derived from the HSV-1 glycoprotein B (gB) protein inhibited HSV-1 infection by specifically targeting paired immunoglobulin-like type 2 receptor alpha (PILRα) in vitro.

Ribophorin II is involved in the tissue factor expression mediated by phosphatidylserine-dependent antiprothrombin antibody on monocytes.

Objective: Phosphatidylserine-dependent, also called aPS-PT, recognizes the phosphatidylserine-prothrombin complex, which is associated with APS. We have previously reported that aPS-PT induces tissue factor (TF) expression on monocytes through the p38 mitogen-activated protein kinase pathway. However, the cell surface interaction between prothrombin and aPS-PT, which is involved in the activation of cell-signalling pathways, has remained unknown.

The immunosuppressive effect of domain-deleted dimer of HLA-G2 isoform in collagen-induced arthritis mice.

HLA-G is involved in maternal-fetal immune tolerance and is reported to be a natural tolerogenic molecule. Seven-spliced isoforms including dimeric and β2m-free forms have been identified. The major isoform, HLA-G1 (and its soluble type HLA-G5), binds to the inhibitory immune receptors, leukocyte immunoglobulin (Ig)-like receptor (LILR) B1 and LILRB2.

Effect of hydrophobic scaffold on the cellular uptake and gene transfection activities of DNA-encapsulating liposomal nanoparticles via intracerebroventricular administration.

Efficient DNA carriers are needed as a gene medication for curing brain disorders. In the present study, the function of a neutral lipid envelope-type nanoparticle (LNP) encapsulating pDNA was evaluated after intracerebroventricular administration. The lipid envelope was composed of a series of SS-cleavable and pH-activated lipid like materials (ssPalm) including myristic acid, vitamin A and vitamin E in the hydrophobic scaffold (LNPssPalmM, LNPssPalmA, LNPssPalmE, respectively).

Crystal structure of extracellular domain of human lectin-like transcript 1 (LLT1), the ligand for natural killer receptor-P1A.

Emerging evidence has revealed the pivotal roles of C-type lectin-like receptors (CTLRs) in the regulation of a wide range of immune responses. Human natural killer cell receptor-P1A (NKRP1A) is one of the CTLRs and recognizes another CTLR, lectin-like transcript 1 (LLT1) on target cells to control NK, NKT and Th17 cells. The structural basis for the NKRP1A-LLT1 interaction was limitedly understood.

Structural basis for simultaneous recognition of an O-glycan and its attached peptide of mucin family by immune receptor PILRα.

Paired Ig-like type 2 receptor α (PILRα) recognizes a wide range of O-glycosylated mucin and related proteins to regulate broad immune responses. However, the molecular characteristics of these recognitions are largely unknown. Here we show that sialylated O-linked sugar T antigen (sTn) and its attached peptide region are both required for ligand recognition by PILRα.

Allosteric regulation of epoxide opening cascades by a pair of epoxide hydrolases in monensin biosynthesis.

Multistep catalysis of epoxide hydrolase/cyclase in the epoxide opening cascade is an intriguing issue in polyether biosynthesis. A pair of structurally homologous epoxide hydrolases was found in gene clusters of ionophore polyethers. In the epoxide opening reactions with MonBI and MonBII involved in monensin biosynthesis, we found that MonBII and catalytically inactive MonBI mutant catalyzed two-step reactions of bisepoxide substrate analogue to afford bicyclic product although MonBII alone catalyzed only the first cyclization.

NKG2D triggers cytotoxicity in murine epidermal γδ T cells via PI3K-dependent, Syk/ZAP70-independent signaling pathway.

Murine epidermal γδ T cells, known as dendritic epidermal T cells (DETCs), survey tissue stress through the invariant T-cell receptor (TCR) and non-clonotypic receptors such as NKG2D. NKG2D signaling via the DAP10-phosphatidylinositol 3-kinase (PI3K) pathway directly stimulates cytotoxicity in natural killer (NK) cells and costimulates CD8(+) T cells to augment TCR signals. In activated murine NK cells, NKG2D signals also via the DAP12-Syk/ZAP70 pathway that triggers both cytotoxicity and cytokine production.

Structural and functional mosaic nature of MHC class I molecules in their peptide-free form.

Despite well-organized peptide-loading mechanisms within the endoplasmic reticulum, major histocompatibility complex class I (MHC-I) molecules can be displayed on cell surfaces in peptide-free forms. Although these empty MHC-I (eMHC-I) molecules are presumably involved in physiological and pathological processes, little is known about their structures and functions due to their instability. Using bacterially expressed HLA-Cw*07:02 heavy chain and β2 microglobulin molecules, we successfully established an in vitro refolding method to prepare eMHC-I molecules in sufficient quantities for detailed structural analyses.

Molecular recognition of paired receptors in the immune system.

Cell surface receptors are responsible for regulating cellular function on the front line, the cell membrane. Interestingly, accumulating evidence clearly reveals that the members of cell surface receptor families have very similar extracellular ligand-binding regions but opposite signaling systems, either inhibitory or stimulatory. These receptors are designated as paired receptors.