The NGF domain (IPR002072, PFAM: PF00243) is a protein present in vertebrates and various snake venoms. It has been shown to induce sympathetic nerves and embryonic sensory neurons to divide and differentiate. Although these proteins have little in common in terms of sequence, they all have a unique arrangement of six cysteines. These cysteines are linked to form a conformation known as the "cystine knot." These proteins are active in dimer form, whether homodimer or heterodimer. The EGF-like structure (IPR000742) first binds with high affinity to specific cell surface receptors. It then induces itself dimerization, which is required for activating tyrosine kinases in the receptors' cytoplasmic domains. Thereby it initiates DNA synthesis and signal transduction of cell proliferation. TGF_BETA 2 (IPR001839) is a growth factor that transforms. TGF-(Transforming Growth Factor) is a multifunctional peptide that regulates the proliferation, differentiation, and other functions of a wide variety of cell types. The TGF-family proteins are only active in homodimers or heterodimers. TGF-signaling pathway dysregulation can result in tumor growth. Cys_knot_C (IPR006207), the functional of the CTCK domain. It is a dimer, whether homodimer or heterodimer. They share essentially minimal sequence homology with an six-cysteine structure. These cysteines are linked to form a conformation known as the "cystine knot." It is the most recently determined crystal structure of four growth factors: nerve growth factor, transforming growth factor, platelet-derived growth factor, and human chorionic gonadotropin.