TABLE 2.

Full list of interactions between Arg⁶⁷² in WT MyHC-emb and the two Arg⁶⁷² mutants

There are interactions between Arg⁶⁷², on β3, and Cys¹²³ and Thr¹²⁵, on β2, of the central β-sheet in most conformations, the exception being the contact to Cys¹²³ in the near rigor, ADP-bound state (PDB 1sS5gG). These interactions are predicted to be conserved in the R672C and R672H mutations. A π-cation bond that exists between Arg⁶⁷² and Phe¹²² (β2) in the rigor state (2osOS8) is lost in both mutations, but a novel π-π bond is formed between R672H and Phe¹²² in the rigor state (20sOS8). The hydrogen bond between Arg⁶⁷² and Leu¹⁷⁶ (β1) is also lost in both mutations in the rigor state. Thr¹⁷⁸ (on β4) hydrogen-bonds to Arg⁶⁷² in each structure; however, this interaction is lost in the post-rigor (1srSR6) and the detached (1kkKK8) states for R672H and is lost completely for R672C. A second significant loss of interaction is the π-cation bond between Arg⁶⁷² and Phe⁴⁹⁰ on the relay helix, which is non-existent in either mutation. A π-cation bond to Phe⁶⁷⁰ is lost for both mutations in the detached state; however, a π-π bond is formed in the pre-power state (1qviQVI). A hydrogen bond between Val⁶⁷¹ is present in WT MyHC-emb in the rigor and post-rigor states (1osOS8, 2otgOTG, and 1srSR6) but lost in both mutations. The hydrogen bond between Asn⁶⁹⁷ on the SH1-SH2 domain is conserved in all three models in the near rigor ADP-bound state (1sS5Gg). However, this is lost in R672H in the detached state (1kkKK8) and in R672C in the post-rigor state (1srSR6). Interestingly, this interaction is formed in both mutants in the rigor (1kkKK8) and post-rigor (2OTGotg) states.