Circular dichroism (CD) stability analyses of EIAV gp45 and its mutant proteins. (A) The sequence alignment of the NHR region for both EIAV gp45 and HIV gp41 is shown. The mutants LN40 and FDDV4 refer to the sequences of the EIAV WT and vaccine strains, respectively. Two HIV sequences, one typical clade B (HXB2) and the other from CRF07 circulating in China, are aligned against EIAV. The a and d positions are highlighted in orange and green shadows, respectively. (B) Secondary structures of the EIAV gp45 protein and its mutants as characterized by CD, at room temperature. The α-helices of gp45 are well-retained across all mutants. (C) Temperature sensitivity measurements. Thermostability of gp45 and its mutants was monitored by CD at 222 nm, along a temperature gradient. (D) Secondary structures of the EIAV gp45 from the vaccine strain, FDDV4, and its mutants characterized by CD, at room temperature. (E) Temperature sensitivity measurements of EIAV gp45 from the vaccine strain FDDV4 and its mutants. Thermostability was monitored as described above. Results are an average of three independent experiments.