. Author manuscript; available in PMC: 2022 Sep 2.

Published in final edited form as: Nat Struct Mol Biol. 2022 Mar 2;29(3):229–238. doi: 10.1038/s41594-022-00735-5

Table 1.

Rates of interconversion between the A (prefusion) and B (open trimer) conformations of spike ectodomains.

Temperature	Protein	k_observed (hr⁻¹)	t_1/2 (hours)
37 °C→4 °C	S-2P	0.04	17
	HexaPro	0.005	143
	Alpha S1 HexaPro	0.2	4
	S-2P + 3A3	0.1	5
37 °C→10 °C	S-2P	0.05	14
	HexaPro	0.004	171
	Alpha S1 HexaPro	0.1, 0.2 ^(*)	3, 5 ^(*)
4 °C→ 37 °C	S-2P	0.08	9
	HexaPro	0.3	2
	Alpha S1 HexaPro	0.2	4

^(*)

Time course was monitored twice, and the results of each fit are reported.

k_observed is the observed rate of change in the population of the A state after a temperature jump. This relaxation rate is the sum of the forward and reverse rates, which is dominated by the major conformational change (A→B at 4 °C, 10 °C and B→A at 37°C). t_1/2 is the half time for that same rate, ln2/k_obs).