The crystal structure of these residues reveals that crossing antiparallel РћВ±-helices and a continuous hydrophobic core maintained by aromatic and bulky hydrophobic amino-acid side chains contribute to the rigidity of the protein (9).Р”Р‡or the first comparison protein, synapse-enriched clathrin adaptor protein (pdb ID=1HX8) (AP-180) has 81% identical sequencing identity with CALM. The residues 1210-1516 in the hub domain mediate spontaneous clathrin heavy-chain polymerization as hub fragment folds into an elongated coil of РћВ±-helices. A terminal domain of clathrin covers residues 1-~479 and functions in AP-2 binding (3). A distal leg domain of clathrin covers residues ~523-1073 and are involved in a cage assembly. Three C-terminal heavy chains of clathrin cover residues 1615-1675 containing Pro-Lys rich motifs. The heavy chains of clathrin are involved in its interactions with the light chains, with other clathrin molecules, and with adopter proteins. CALM is structurally similar to the epsin NH2-terminal domain but epsin does not contain PtdIns(4,5)P2-binding site (1).Р”Р„ triskelion-shaped clathrin (pdb ID=1xi4) is composed of a trimer of heavy-chain subunits of 1,675 residues, each binding a single light chain subunit in the hub domain, which covers residue 1074-1675. The РћВ±1-РћВ±2 loop regions appear on the three protein familes including CALM/AP-180 family and some other proteins with the PtdIns(4,5)P2-binding motif, and epsin family. The clathrin-box motif is mostly located in a helix. The secondary structure of CALM is 59% alpha-helical, with 11 helices and 171 residues. The cluster of lysines and a histidine forms a positively charged patch, which is ideal for phosphate-binding protein (1). Compared to typical ligand-binding sites of a pocket or groove of protein, CALM has its binding site on the surface, with the phosphates rested on the tips of the side chains of three lysines and a histidine. Its ligand provides a binding site for AP-180 and clathrin, serving to tether clathrin to the membrane. The ligand component of CALM is phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2). The molecular weight of CALM is 32823.80 Da, and its isoelectric point (pI) is 9.07.Р”В¬ALM consists of subunit A and one ligand. A binding of 1-phosphatidylinositol occurs where clathrin selectively and non-covalently interacts with phosphatidlinositol. AP-2 binds to the terminal domain region of the clathrin molecule. For example, CALM protein is involved in AP-2-dependent clathrin-mediated endocytosis at the neuromuscular junction (2). Phosphatidylinositol-binding clathrin assembly protein (pdb ID=1HFA) (alternative name: Clathrin assembly lymphoid myeloid leukemia protein (CALM) ) from Rattus norvegicus is an assembly protein recruiting clathrin and adaptor proteins to cell membranes at sites of coated-pit formation and clathrin-vesicle assembly. Clatherin Assembly Lymphoid Myeloid Leukemia Protein (CALM)

Bulky hydrophobic amino acids