Table 1.

Nomenclature, localization and functional importance of T4SS proteins encoded by the cagPAI of Helicobacter pylori.

Gene name†	Protein name‡	Size (kDa)†	Subcellular localization§	Structure data	Phospho CagA¶	IL-8 secretion#	T4SS pilus formation††	Proposed function§
hp0520	Cagζ/Cag1	13	IM	n.d.	+++	+++	n.d.	AF
hp0521	Cagε/Cag2	10	Cyt	n.d.	+++	+++	n.d.	AF
hp0522	Cagδ/Cag3	50	OM	n.d.	–	–	–‡‡	OM complex
hp0523	Cagγ/Cag4	18	Per	n.d.	–	–	n.d.	VirB1, PGN hydrolase
hp0524	Cagβ/Cag5	80	IM	n.d.	–	+++	+++‡‡	VirD4, coupling factor
hp0525	Cagα/VirB11	35	Cyt, IM	Yes [18]	–	–	+++‡‡	VirB11, NTPase
hp0526	CagZ	21	Cyt, IM	Yes [19]	++	++	n.d.	Cagβ stabilization
hp0527	CagY	220	IM, OM, SA	n.d.	–	–	–‡‡,§§	VirB10, core complex, integrin binding
hp0528	CagX	55	IM, OM, SA	n.d.	–	–	¶¶,‡‡	VirB9, core complex
hp0529	CagW	55	IM	n.d.	–	–	n.d.	VirB6, IM channel
hp0530	CagV	27	IM	n.d.	–	–	–¶¶	VirB8, core complex
hp0531	CagU	23	IM	n.d.	–	–	n.d.	AF
hp0532	CagT	30	OM, SA	n.d.	–	–	–¶¶,‡‡,##	VirB7, core complex, OM lipoprotein
hp0534	CagS	21	Cyt	Yes [20]	+++	+++	n.d.	AF
hp0535	CagQ	14	IM	n.d.	+++	+++	n.d.	AF
hp0536	CagP	13	IM	n.d.	+++	+++	n.d.	AF
hp0537	CagM	40	OM	n.d.	–	–	–¶¶	OM complex
hp0538	CagN	32	Per, IM	n.d.	+	+	n.d.	Accessory factor
hp0539	CagL	26	Per, SA	Yes [21]	–	–	–†††,##	Pilus biogenesis, VirB5-like, integrin targeting
hp0540	CagI	40	Per, SA	n.d.	–	–#	–##	Pilus biogenesis, integrin targeting
hp0541	CagH	39	IM	n.d.	–	–	++++##	Pilus biogenesis
hp0542	CagG	16	Per	n.d.	–	++	n.d.	AF
hp0543	CagF	29	Cyt, IM	n.d.	–	+++	n.d.	Chaperone of CagA
hp0544	CagE	100	IM	n.d.	–	–	–##	VirB3/VirB4, NTPase
hp0545	CagD	22	IM, Per, SA	Yes [22]	+	+‡‡‡	n.d.	Accessory factor
hp0546	CagC	13	IM, OM, SA	n.d.	–	–	+++¶¶	VirB2, pilus subunit?
n.d.	CagB	8	Cyt	n.d.	n.d.	n.d.	n.d.	AF
hp0547	CagA	125	Cyt, SA	Yes [23,24]	–	+++	n.d.	Translocated effector

^†Gene designations and corresponding protein sizes are according to H. pylori strain 26695 [GenBank:AE000511.1].

^‡Cag protein designations are according to a previous study [11].

^§Subcellular localization of cagPAI proteins and proposed functions were reviewed by a previous article [11].

^¶Phosphorylation of CagA and IL-8 induction in the corresponding cag gene knockout mutants of strain 26695 are listed according to a previous study [23]. Abbreviations used for the observed responses: -: Abolished; +: Weak; ++: Moderate; +++: Strong (like wild-type).

^#Corrected data with regard to requirement for IL-8 induction [25].

^††T4SS pilus formation in the corresponding knockout mutants are according to numerous previous studies listed below. Abbreviations used for pilus formation compared with wild-type H. pylori: -: Abolished; + : Weak; ++: moderate; +++: Unchanged; ++++: Hyperpiliated.

^‡‡T4SS pilus formation in strain NCTC11637 and corresponding knockout mutants are according to Tanaka and coworkers [26].

^§§Conflicting data exist with regard to T4SS pilus formation in the corresponding cagY knockout mutant in strain J166 [27].

^¶¶T4SS pilus formation in strain 26695 and corresponding knockout mutants are according to Johnson and coworkers [28].

^##T4SS pilus formation in strain 26695 and corresponding knockout mutants are according to Shaffer and coworkers [29].

^†††T4SS pilus formation in strain P12 and the corresponding cagL knockout mutant are according to Kwok and coworkers [9].

^‡‡‡Conflicting data exist with regard to requirement for CagA phosphorylation [22,30].

AF: Accessory factor with yet unknown function; Cyt: Cytoplasmic; IM: Inner membrane; n.d.: Not determined; OM: Outer membrane; Per: Periplasmic; PGN: Peptidoglycan; SA: Surface associated or secreted into the supernatant; T4SS: Type IV secretion system.