Figure 2. The human receptor tyrosine kinase superfamily. This shows the modular structure of the various subfamilies of RTKs encoded in the human genome. Note that the AATYK family of three kinases is now considered a serine/threonine kinase (17), which leaves 55 RTKs grouped into 19 families. The various modules that constitute the architecture of the extracellular and intracellular domains are shown below. A detailed description of the structure of these modules can be found in reference 22. From reference 22, used with permission.