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Biotinylated proteins are a class of labeled proteins formed by covalently attaching biotin to proteins through chemical or enzymatic methods. The Biotin-Avidin System is a commonly used biological signal amplification system introduced into the field of immunology in the late 1970s, renowned for its high specificity, high sensitivity, and high stability. The affinity constant between biotin and avidin is as high as 10^15 mol/L, which is at least 10,000 times higher than that of antigen-antibody interactions and represents the strongest known non-covalent interaction. This makes biotinylated proteins powerful tools for studying protein-protein interactions and for screening antibodies or small molecule drugs. Based on their high affinity and signal amplification capacity, biotinylated proteins have been widely applied in various experimental detection platforms, including ELISA, flow cytometry, biopanning, surface plasmon resonance, and biolayer interferometry. Biotinylated proteins play an indispensable role in clinical diagnostics, antibody drug screening, cell therapy target validation, and vaccine development, making them important tools in the field of biomedical research.

Immune checkpoint proteins are a class of key membrane proteins located on the surface of immune cells or tumor cells that regulate the intensity of immune responses. By binding to their corresponding ligands or receptors, they transmit co-stimulatory (activating) or co-inhibitory (suppressing) signals to immune cells, thereby maintaining immune homeostasis and preventing autoimmune reactions. Among them, co-inhibitory checkpoint proteins represented by PD-1, PD-L1, and CTLA-4 normally act as the ""brakes"" of the immune system, ensuring that immune responses do not excessively damage healthy tissues. However, tumor cells can exploit these immune checkpoint proteins to suppress T cell activity and achieve immune evasion, for instance by overexpressing PD-L1. To counter this mechanism, monoclonal antibody drugs targeting immune checkpoints (such as anti-PD-1, anti-PD-L1, and anti-CTLA-4 inhibitors) can block the transmission of inhibitory signals and reactivate the immune system to attack tumors. Currently, immune checkpoint inhibitors have become a cornerstone of cancer immunotherapy, demonstrating remarkable efficacy in the treatment of various malignancies, including melanoma, non-small cell lung cancer, and renal cell carcinoma. Furthermore, soluble immune checkpoint proteins, as biomarkers in serum, are also used to monitor immunotherapy responses and assess patient prognosis.

Virus-like particles (VLPs) are nanoscale particles, typically ranging from 20 to 200 nanometers in diameter, formed by the self-assembly of one or more viral structural proteins. As they lack viral genetic material, VLPs are replication-incompetent and non-infectious, offering significant advantages in biosafety. VLPs closely mimic the morphology and antigenic epitope presentation of native viruses. The repetitive, high-density array of epitopes on their surface effectively activates both innate and adaptive immune responses, inducing robust humoral and cellular immunity. Based on their excellent immunogenicity and engineerability, VLPs have become a prominent platform for vaccine development and targeted drug delivery. Several VLP-based vaccines have been approved and marketed, including those against hepatitis B virus, human papillomavirus, and hepatitis E virus. In addition, VLPs serve as a membrane protein display platform, where full-length transmembrane proteins with native conformations are presented on the VLP surface, enabling applications in immunization, antibody screening, and CAR-T cell therapy target validation. In the field of targeted drug delivery and gene therapy, VLPs are also being engineered to encapsulate therapeutic cargoes such as small molecule drugs, siRNA, mRNA, and CRISPR-Cas gene editing systems, demonstrating broad application prospects.

Target proteins refer to biological macromolecules, predominantly proteins, that can be specifically recognized and bound by drug molecules to elicit therapeutic effects. As the starting point for drug discovery, target proteins encompass a diverse range of functional classes, including classical enzymes, receptors, ion channels, and transporters. They play central roles in physiological processes such as signal transduction, metabolic regulation, and immune responses, with their dysfunction often serving as the molecular basis of diseases. Based on their well-established disease associations, target proteins are essential tools in drug discovery and clinical diagnostics. In research workflows, recombinant target proteins are widely utilized for antibody screening (e.g., monoclonal/bispecific antibodies), CAR-T cell therapy target validation, and high-throughput drug screening model development. The scope of target proteins is extensive, encompassing well-studied immune checkpoints (e.g., PD-1) and cytokines, as well as hard-to-classify secreted regulatory proteins and intracellular signal transducers, serving as a bridge linking genomics to precision medicine.

Viral antigens are components of viral structural proteins that can be specifically recognized by the host immune system and induce immune responses. They mainly include viral surface proteins (such as spike protein, hemagglutinin, and envelope protein) and internal proteins (such as nucleoprotein and capsid protein). As the bridge between viruses and their hosts, viral antigens play a critical role in viral entry, replication, and transmission, while serving as the primary targets for the body to generate protective immune responses. Viral antigens are core reagents in infectious disease research and biopharmaceutical development. In vaccine development, recombinant viral antigens are widely used to design subunit vaccines and virus-like particle vaccines. In diagnostics, viral antigens are key components of immunoassay kits, enabling the development of ELISA and lateral flow assays for rapid screening of viral infections. Furthermore, viral antigens are extensively applied in antibody screening, antiviral drug development, and quality controls in serological assays. With high purity and rigorous quality control standards, recombinant viral antigens have become indispensable tools in infectious disease research.

GMP proteins are recombinant protein products manufactured and managed in accordance with Good Manufacturing Practice requirements. Unlike research-grade proteins, GMP-grade proteins are produced under stringent quality control systems, including raw material testing, equipment validation, personnel training, process control, and documentation management, ensuring product safety, consistency, traceability, and lot-to-lot stability. GMP proteins typically feature extremely low endotoxin levels (≤0.1 EU/μg) and undergo comprehensive biological activity validation. Based on their high-quality manufacturing standards, GMP proteins are primarily used in the research and production of clinical-grade products such as cell therapies, gene therapies, and tissue engineering. In processes such as CAR-T cell preparation, stem cell expansion, and immune cell culture, GMP-grade cytokines and growth factors serve as critical ancillary materials, enabling seamless transition from preclinical research to clinical manufacturing. GMP proteins cover a wide range of cytokines including IL-2, IL-7, IL-15, GM-CSF, SCF, FGF-basic, and TNF-α, broadly supporting research and development in tumor immunotherapy, regenerative medicine, and gene editing.

Based on their diverse functions and application scenarios, recombinant proteins have become important tools in fundamental life science research and biopharmaceutical application development.

Transmembrane proteins are a class of proteins embedded in the phospholipid bilayer of cell membranes, enabling crossing between the intracellular and extracellular environments. The interactions within the transmembrane region serve as crucial channels connecting the extracellular environment with the intracellular environment, thereby executing various activation and response reactions to achieve signal transduction and regulate morphological and functional changes both inside and outside the cell. Many human diseases are closely associated with dysfunction of transmembrane proteins. The multifunctional nature of transmembrane proteins makes them ideal drug targets. To date, numerous drugs targeting transmembrane proteins (such as G protein-coupled receptors and ion channels) have been successfully developed and are widely used in the treatment of cancers, cardiovascular diseases, and neurological disorders.

Enzymes are a class of protein catalysts that facilitate biochemical reactions in living organisms. By significantly reducing the activation energy required for reactions, enzymes accelerate the conversion of substrate molecules into product molecules without being consumed in the process. They play an indispensable role in nearly all physiological processes, including metabolism, DNA replication, signal transduction, and detoxification, and are widely present in various tissues and cell types throughout the human body. Due to their central role in regulating biological functions, dysfunction or dysregulation of enzymes is closely associated with numerous human diseases, including cancer, neurodegenerative disorders, inflammatory diseases, and metabolic syndromes. Enzymes have therefore become important targets for drug development, as well as key tools in clinical diagnostics and industrial biotechnology. Currently, enzyme inhibitors such as kinase inhibitors, protease inhibitors, and reverse transcriptase inhibitors have been successfully developed for the treatment of cancers, viral infections, cardiovascular diseases, and other conditions.

Cytokines are a class of biologically active low-molecular-weight polypeptides, proteins, or glycoproteins that are synthesized and secreted by immune cells (such as monocytes, macrophages, T cells, B cells, and NK cells) and non-immune cells (such as vascular endothelial cells, epidermal cells, and fibroblasts) upon stimulation. They exert a variety of biological functions, including maintaining cell survival and proliferation, inducing cell differentiation, regulating innate and adaptive immunity, and exhibiting antiviral activity. Based on their functions, cytokines are classified into interleukins, colony-stimulating factors, interferons, the tumor necrosis factor superfamily, chemokines, growth factors, and others.