TABLE 2.

Summary of major protein response of Synechococcus sp. to l-homopropargylglycine^a

Physiological response (reference[s])	Description of response	Protein(s)	+/−	Reference(s)b
General protein stress	Stressful conditions inside cell cause protein misfolding and aggregation. Increased expression of chaperone proteins is part of the core stress response in cyanobacteria.	60-kDa chaperonin 1 (GroEL, sync_2135)	+	38
		60-kDa chaperonin 2 (GroEL2, sync_2282)	+
		Chaperone protein (HtpG, sync_1398)	+
		Chaperone protein (DnaK, sync_2923)	+
Interference with nitrogen cycling	Cells are trying to boost the glutamine synthetase/glutamate synthetase (GS/GOGAT) cycle to get ammonium into carbon skeletons and distribute N throughout the cell. Enzymes are potentially inhibited by HPG, causing interference with N cycling.	Glutamine synthetase (GlnA, sync_1569) Ferredoxin-dependent glutamate synthetase (FdGOGAT, sync_0387)	+ +	35, 36, 37
Interference with energy production	Increasing energy production by increasing ATP synthase subunits.	ATP synthase proteins (AtpH, sync_2314; AtpF, sync_2315)	+	45
		ATP synthase F1 subcomplex beta subunit (AtpD*, sync_2284)	−
	Upregulating major components of photosystem I to potentially increase energy production via this reaction center.	Photosystem I proteins (PsaA, sync_0393; PsaB, sync_0394; PsaC*, sync_0133; PsaD, sync_0463; PsaF*, sync_2155; PsaL, sync_0398)	+	43
	Increasing antenna proteins of phycobilisome, especially linker proteins, to potentially increase light energy harvest by this complex. Linker proteins are especially important because they ensure proper assembly of phycobiliproteins and improve unidirectional energy flow from the outer antennae to the core.	Phycoerythrin class II gamma chain, linker polypeptide (CpcC, sync_0502)	+	41, 49
		Phycobilisome linker polypeptide* (CpcD, sync_0512)	+
		Phycobilisome rod-core linker polypeptide (CpcG1, sync_2488)	+
		Possible phycobilisome rod-core linker polypeptide (CpcG, sync_0515)	+
		Possible phycobilisome linker polypeptide (sync_0516)	+
		Phycobilisome linker polypeptide (CpeC, sync_0513)	+
		Possible phycobilisome linker polypeptide (CpeD1, sync_0511)	+
		Phycobilisome linker polypeptide (CpeD2, sync_2251)	+
		C-phycoerythrin class I beta chain (CpaB1*, sync_0495)	+
		C-phycoerythrin class II alpha chain (CpaA2*T, sync_0504)	+
		C-phycoerythrin class II beta chain (CpaB2*T, sync_0505)	+
		Allophycocyanin alpha-B subunit apoprotein (ApcD, sync_1341)	+
		Phycobilisome core-membrane linker protein (ApcE, sync_2321)	+

^aUp- or downregulation indicates a significant difference in both nitrate-replete and nitrate-limited treatments relative to the control treatment (P < 0.05). An asterisk (*) indicates an HPG-labeled protein. A superscript “T” indicates a log₂-fold change of <1 for the pairwise comparisons.

^bReferences apply to each subsection broadly.