CD40, also known as TNFRSF5, is a type I transmembrane protein. The molecular weight of CD40 is 48-kDa and it consists of a 193 amino acid (aa) extracellular domain, 21 aa leader sequence, 22 aa transmembrane domain, and a 62 aa intracellular domain in human (90 aa in mouse).https://www.creative-biolabs.com/adc/target-cd40-122.htm