Table II. Mass spectrometry quantification of proteins enriched in affinity chromatography eluates.

Proteins showing at least a 5 times enrichment in N-His-PSBS eluate compared with psbs KO according to mass spectrometry-based label-free quantification are shown. Each protein was quantified from the average of its three most intense peptides. The content of each protein was normalized to the one in psbs KO. Relative enrichment in N-His-PSBS compared with C-His-PSBS is also shown. LHCBM and LHCB4 include multiple polypeptides that were not individually distinguished, as detailed in “Materials and Methods.” n.d., Protein not detected in at least one replicate. All data are expressed as averages ± se of three independent replicates. Expected mass of the mature protein for each identified protein is also reported. Signal peptide length was estimated with the ChloroP tool and mature protein mass with the Compute pI/Mw tool (Expasy).

Uniprot Accession	Mass	Annotation	N-His-PSBS	C-His-PSBS	psbs KO	N-His-PSBS/C-His-PSBS
	kD
A9TJ15	23	PSBS			n.d.	3.60 ± 0.60
A9T914, A9SGM1, A9S6S7, A9TL35, A9RT62, Q765P5, A9RJS3	24.8	LHCBM	5.69 ± 1.35	1.85 ± 0.07	1	3.07 ± 0.43
A9U3M1, A9T2F8	28	LHCB4	8.48 ± 3.90	1.66 ± 0.30	1	5.12 ± 1.46
A9TL15	36.9	PpCAS1	7.12 ± 1.16	3.17 ± 0.63	1	2.25 ± 0.33
A9TKU6	25	LHCB3	6.85 ± 1.55	1.90 ± 0.15	1	3.60 ± 0.50
A9SC57	74	Uncharacterized protein	7.14 ± 0.92	2.70 ± 0.47	1	2.65 ± 0.33
A9TW76	39.3	CAS3	8.94 ± 2.19	4.28 ± 0.52	1	2.09 ± 0.33
A9SZ30	40.2	PpCAS2			n.d.	2.87 ± 0.57
A9TEL5	48	PTOX1			n.d.	2.29 ± 0.30