Synthesis and Structure
IL-1α is a unique member in the cytokine family in the sense that the structure of its initially synthesized precursor does not contain a signal peptide fragment (same is known for IL-1β and IL-18). After processing by the removal of N-terminal amino acids by specific proteases, the resulting peptide is called "mature" form. Calpain, a calcium-activated cysteine protease, associated with the plasma membrane, is primarily responsible for the cleavage of the IL-1α precursor into a mature molecule. Both the 31kDa precursor form of IL-1α and its 18kDa mature form are biologically active.
The 31 kDa IL-1α precursor is synthesized in association with cytoskeletal structures (micro-tubules), unlike most proteins, which are translated in the endoplasmic reticulum.
The three-dimensional structure of the IL-1α contains an open-ended barrel composed entirely of beta-pleated strands. Crystal structure analysis of the mature form of IL-1α shows that it has two sites of binding to IL-1 receptor. There is a primary binding site located at the open top of its barrel, which is similar but not identical to that of IL-1β.
Read more about this topic: IL1A
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