Emerging role of caldesmon in cancer: A potential biomarker for colorectal cancer and other cancers

Figure 1 The domain structures of high-molecular-weight caldesmon and low-molecular-weight caldesmon. Human caldesmon (CaD) has two major isoforms resulting from alternative splicing. The upper bar represents high-molecular-weight CaD (h-CaD) (793 aa), the full length protein, which contains an N-terminal domain (NH₂), a C-terminal domain, and a middle part (repeating domain). The lower bar represents low-molecular-weight CaD (l-CaD) (538 aa), which is missing the middle repeating region. All functional domains are shared between h-CaD and l-CaD, except the missing central spacer in l-CaD that separates the N-terminal myosin binding domain from the C-terminal actin binding domain. Common functional regions for myosin and calmodulin are located within the NH₂ terminal. The calmodulin binding site is also located in the C-terminal region. Tropomyosin and actin binding sites are found in the C-terminal region. Phosphorylation sites are shown and the shared phosphorylation sites for ERK and cdc2 are highlighted (yellow). h-CaD: High-molecular-weight caldesmon; l-CaD: Low-molecular weight caldesmon; NH₂: N-terminal domain; COOH: C-terminal domain.