CALML4 (Calmodulin-Like Protein 4) is a small EF-hand protein encoded by the CALML4 gene located at human chromosome 15q23, which functions primarily as a myosin light chain within the intermicrovillar adhesion complex (IMAC) essential for epithelial brush border differentiation, where it binds to the neck region of the motor protein MYO7B to mediate microvilli organization and length control. Structurally, the longest isoform comprises 196 amino acids with a bilobed EF-hand architecture (N-lobe and C-lobe) and calcium‑binding capacity, although five alternatively spliced isoforms exist, some lacking an intact N-lobe. CALML4 is broadly expressed, with highest levels in the colon and duodenum, and is localized at the distal tips of intestinal microvilli. Clinically, common genetic variants in CALML4 have been investigated for their association with antidepressant efficacy in major depressive disorder, while its role in brush border assembly underscores its physiological importance in intestinal epithelia.