Figure 1. Structures of the Ca-ATPase and PLB.

Structure of the Ca-ATPase (1su4.pdb) depicts headpiece, corresponding to discrete structural elements associated with the A-domain (residues 1-43 and 124-235; purple), N-domain (residues 360-600; pink), and P-domain (residues 330-359 and 601-739; green) relative to the transmembrane helices TM1-TM2 (residues 44-123; cyan), TM3-TM6 (residues 239-329 and 740-821, red), and TM7-TM10 (residues 831-994; gray), where domain boundaries are as previously described (72). The ten NMR structures of a PLB monomer are shown on the right (1fjk.pdb). Highlighted in the structures of Ca-ATPase and PLB are (yellow space-filling) side chains that have been identified through covalent cross-linking experiments which involve both endogenous amino acids (C or K) or engineered cysteines at sites in TM2 (i.e., V⁸⁹), TM4 (T³¹⁷, C³¹⁸, L³²¹, and K³²⁸), and the N-domain (i.e., K³⁹⁷DDKPV⁴⁰²) of the Ca-ATPase with sites on PLB (i.e., I⁴⁵-L⁵², L³¹, N³⁰, N²⁷, Q²³, or K³) (9-11). Labeling sites are indicated for FITC modification at K⁵¹⁴ /K⁵¹⁵ in the N-domain (blue oval) and IAF modification at C⁶⁷⁴ in the P-domain (red oval) of the Ca-ATPase.