Table 3 Isopeptides between TG2 and peptides derived from barley gluten protein types.

Abb.^a	TG2 lysine^b	Gluten peptide^c	GPT^d	UniProtKB accession	UniProtKB name	Organism	MQ score^e	Fragments (discovery)^f		Manually checked (discovery)^g		Fragments (targeted)^h
Abb.^a	TG2 lysine^b	Gluten peptide^c	GPT^d	UniProtKB accession	UniProtKB name	Organism	MQ score^e	α ⁱ	β^j	α	β	α	β
B1 ^l	K205	QGQQGQQLGQGQQGYY	D	A0A2C9PIB7	high-molecular-weight glutenin subunit protein	Ae. umbellulata	59.90	13	—	25	4	16	—
B2	K265	VQQQQPPF	B	V9P6N2	LMW-i glutenin subunit 1	T. aestivum	85.85	8	2	9	1	8	2
B3	K590	PQQPGQW	D	I6TRS8	D-hordein	H. vulgare	44.97	7	13	11	21	7	13
B4	K590	IIPQQPQQPFPLQPHQPY^k	γh	P17991	C-hordein	H. vulgare	44.20	10	7	17	10	11	7
B5	K600	PQQPGQGQQPGQR	D	I6TRS8	D-hordein	H. vulgare	121.20	19	—	31	2	14	—
B6	K600	PQQPGQGQGQQGYYPGATSL^k	D	I6TRS8	D-hordein	H. vulgare	82.36	18	—	35	—	24	—
B7^l	K677	PLQPQQPFPW	γh	Q41210	C-hordein	H. vulgare	72.55	9	1	23	3	8	1
B8	K677	PQQQFPQQQFHQQQL	γh	A0A0B5JD29	omega-gliadin	T. aestivum	52.73	12	—	36	4	16	1
B9^l	K677	FPQYQIPTPL	γh	Q40053	Hor1–17 C-hordein	H. vulgare	47.94	11	2	25	7	10	2
B10^l	K677	PQQPGQGQGQQGYYPGATSL	D	I6TRS8	D-hordein	H. vulgare	106.36	23	2	41	3	24	2

^aAbb., abbreviation, ^bLysine residue in the TG2 sequence, K205: peptide FLKNAGR, K265: peptide WKNHGCQR, K590: DLYLENPEIKIR, K600: QKR, K677: AVKGFR, ^cGlutamine residues involved in crosslinking to TG2 are highlighted in bold, deamidation sites underlined, ^dGPT, gluten protein type, D, D-hordeins, B, B-hordeins, γh, γ-hordeins, ^eMQ, MaxQuant, ^fNumber of fragments identified by discovery-driven nLC-MS/MS and MaxQuant data analysis, ^gNumber of fragments identified by discovery-driven nLC-MS/MS and manual inspection of full scan spectra considering additional internal fragments calculated by ProteinProspector, ^hNumber of fragments identified by PRM analysis, ⁱα, α-side of the isopeptide (gluten peptide), ^jβ, β-side of the isopeptide (TG2 peptide), ^kBoth crosslinking sites are possible and could not be identified unambiguously due to missing fragments, ^lCrosslinking site identified by PRM analysis.

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