Table S5.

Peptides and modification sites detected by XF-MS, and the ratio(s) of hydroxyl radical reactivity for OCP^R versus OCP^O

Seq. no.*	Peptide sequence†	Site of modification‡	Ratio “R“ of hydroxyl radical reactivity kOCPR/kOCPO§
2–9	PFTIDSAR	P2, F3 (+16 Da)¶	0.74 ± 0.15
		A8, R9 (+16 Da)	1.85 ± 0.39
10–27	GIFPNTLAADVVPATIAR	Residues 13–22 (+16 Da)	1.93 ± 0.25
28–49	FSQLNAEDQLALIWFAYLEMGK	W41 (+48 Da)	0.35 ± 0.05
		W41, F42, Y44, M47 (+16 Da)	0.47 ± 0.09
		M47 (+16 Da)	0.76 ± 0.16
50–69	TLTIAAPGAASMQLAENALK	A54, A55, P56 (+16 Da)	0.76 ± 0.09
		M61 (+16 Da)	1.06 ± 0.22
70–89	EIQAMGPLQQTQAMCDLANR	M74 (+16 Da)	0.69 ± 0.13
		M74P76M83 (+16 Da)	0.67 ± 0.02
97–106	TYASWSPNIK	Y98W101P103 (+16 and +32 Da)	1.95 ± 0.30
107–112	LGFWY	F109W110Y111 (+16 and +32 Da)	0.90 ± 0.13
113–155	LGELMEQGFVAPIPAGYQLSANANAVLATIQGLESGQQITVLR	M117 (+16 Da)	0.69 ± 0.13
119–146	QGFVAPIPAGYQLSANANAVLATIQGLE	F121,P124,P126 (+16 Da)#	0.17 ± 0.05
147–160	SGQQITVLRNAVVD	R155, N156 (+16 Da)	10.11 ± 3.96
156–167	NAVVDMGFTAGK	M161 (+16 Da)	0.68 ± 0.12
		F163 (+16 Da)	0.78 ± 0.46
		K167 (+16 Da)	0.70 ± 0.21
172–185	IAEPVVPPQDTASR	P175P178P179R185 (+16 Da)	0.58 ± 0.06
192–215	GVTNATVLNYMDNLNANDFDTLIE	M202 (+16 Da)	1.1 ± 0.18
		Residues 119–215 (+16 Da)#	0.89 ± 0.08
221–235	GALQPPFQRPIVGKE	Residues 226–231 (+16 Da)#	0.58 ± 0.07
243–249	EECQNLK	No modification	||
255–268	GVTEPAEDGFTQIK	P259, F264, K268 (+16 Da)	1.02 ± 0.11
273–289	VQTPWFGGNVGMNIAWR	P276, W277, F278 (+32 Da)	2.02 ± 0.23
		M284 (+16 Da)	1.54 ± 0.17
290–297	FLLNPEGK	F190 (+16 Da)	2.16 ± 0.33
		L291, L292 (+16 Da)	0.59 ± 0.05
		P294 (+16 Da)	0.58 ± 0.11
298–310	IFFVAIDLLASPK	I298, F299 (+16 Da)	1.21 ± 0.27
		V301, A302, I303 (+16 Da)	2.08 ± 0.30
		P309, K310 (+16 Da)	0.46 ± 0.07

^*The 94% sequence coverage was obtained from the bottom-up LC-electrospray ionization (ESI)-MS analysis of OCP^O and OCP^R using trypsin and Glu-C digestion.

^†Sequences of digested fragments identified by mass spectrometry analysis described in SI Methods.

^‡Positions of modified residues identified by mass spectrometry analysis described in SI Methods.

^§The ratio (R) of hydroxyl radical reactivity rate between OCP^O and OCP^R from three independent measurements. The rate constants (k s⁻¹) were estimated by using a nonlinear fit of hydroxyl radical modification data to a first order decay as described in SI Methods. R is a quantitative measure of the change in the solvent accessibility.

^¶Mass shift due to side chain modification is show within the parentheses.

^#Side chain modification at multiple residues within the specified sequence number.

^||No ratio of hydroxyl radical reactivity.