TABLE 2.

Average RBD1 and SL2 order parameters (S²) from model-free analysis of experimental relaxation data or RED analysis of simulation trajectories

RBD1	All	2°	Loop 1	Loop 3	TDS
NMR, unbound*	0.84 ± 0.13	0.88 ± 0.04	0.80 ± 0.08	0.87 ± 0.06	0.74 ± 0.07
RED, unbound†	0.78 ± 0.17	0.85 ± 0.04	0.63 ± 0.05	0.78 ± 0.06	0.64 ± 0.06
RED, bound	0.85 ± 0.06	0.86 ± 0.04	0.84 ± 0.03	0.89 ± 0.01	0.87 ± 0.02
SL2	Stem	No fray	Loop	Loop bound	UCC
RED, ribose	0.82 ± 0.16	0.87 ± 0.07	0.79 ± 0.21	0.92 ± 0.01	0.49 ± 0.04
RED, base	0.80 ± 0.14	0.87 ± 0.04	0.76 ± 0.25	0.90 ± 0.04	0.36 ± 0.07

“All” refers to all nonproline, non-N-terminal backbone amides of RBD1.

“2°” are all RBD1 sites found in canonical secondary structures (Fig. 1 a). Leu¹⁷-Ile²¹ (loop 1) connects β1 and αA. Ser⁴⁶-Arg⁵² (loop 3) connects β2 and β3.

“TDS” is T89, D90, and S91, found between β4 and αC.

“Stem” is the 10 nucleotides in the SL2 stem (Fig. 1 b).

“No fray” is nucleotides 2–5 and 16–19.

“Loop” refers to the 10 nucleotides of the loop (Fig. 1 b).

“Loop bound” is the 7 nucleotides starting from the 5′ end of the loop.

“UCC” is the trinucleotide sequence at the 3′ end of the loop.

Values are reported as mean ± SD.

^*(16) Loop 1 average S² does not include Lys²⁰. Loop 3 includes only Ser⁴⁶, Ser⁴⁸, and Met⁵¹. Only TD are included in the TDS average. The missing amides were not visible at pH 6.8.

^†(17)