ABSTRACT
Protein is the major component of all cells in the body and plays numbers of functions in the biological world, from catalyzing chemical reactions to build the structures of all living things. Cell receptors are made up of protein and they play a major role in signal transduction. Out of the many cell receptors, the well-known G-protein-coupled receptors (GPCRs) represent the most important targets in modern pharmacology because of the different functions they mediate, especially within the brain and peripheral nervous system. Other GPCRs like β1-adrenergic receptor (β1AR) that plays a paramount role in chronic heart failure, 5-HT4 receptor and acetylcholine receptor (AChR) has role in the treatment of Alzheimer’s disease (AD), N-methyl-D-aspartate receptor (NMDAR) is a stimuli for neuroautoimmune disorder, dopamine receptor (DAR) improves the stimulants in the treatment of Parkinson’s disease (PD), cannabinoid (CB1 and CB2) receptor in the brain, and are involved in a variety of physiological processes including appetite, pain-sensation, mood, and memory. Adenosine receptor (AR) on erythrocytes reduces the HbS oxygen affinity and promotes its polymerization and red blood cell sickling. Chemokine receptors are cytokine receptor that interacts with the leukocyte cells 2on the surface. Another category of receptor involves receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones, that phosphorylates the cascades of the various signaling pathways. The transforming growth factor-β (TGF-β) system signals via protein kinase receptors and regulates the biological processes, including morphogenesis, embryonic development, adult stem cells differentiation, immune regulation, wound healing, or inflammation. Signaling through platelet-derived growth factor (PDGF) receptors contribute to multiple tumors associated processes. The ErbB/HER protein-tyrosine kinases, which include the epidermal growth factor receptor, are associated with the development of neurodegenerative diseases, such as multiple sclerosis and Alzheimer’s disease. Insulin receptor (IR) plays a key role in glucose homeostasis. Among other receptors in plants, one of them is receptor-like kinases (RLKs) which control a wide range of processes, including development, disease resistance, hormone perception, and self-incompatibility in plants. Toll-like receptors (TLRs) are non-catalytic receptors expressed in sentinel cells and play a key role in the innate immune response to invading pathogens. Apart from cell surface receptors, there is a nuclear receptor (NR) that regulates transcription in response to small lipophilic compounds and plays a role in every aspect of development, physiology, and disease in humans. Nuclear receptor (NR) includes estrogen (ERNR), progesterone (PRNR), androgen (ARNR), Vitamin D (VDRNR), and thyroid hormone (TRNR) receptors. In this chapter, we focus mainly on a signaling pathway of various receptors and their significance in various human ailments.
