Table 1.

Functional classification of proteins common in all PPDs

	Gene symbol	Description	Function	Reference
1	AcpP	Acyl carrier protein	It shuttles the intermediates between the enzymes of type II fatty acid synthase system	[31]
2	FbpA	Secreted antigen 85-A	It participates in cell wall biosynthesis, and interacts with the host macrophage as fibronectin-binding protein. It is also involved in establishment and maintenance of a persistent tuberculosis infection	[32,33]
3	GroES	Co-chaperonin	It is a dominant immunogenic protein	[34]
4	DnaK	Molecular chaperone	It is highly antigenic and act as co-repressors for heat shock protein transcriptional repressor (hspR)	[35]
5	Tpx	Thiol peroxidase	It protects M. tuberculosis against oxidative and nitrosative stress	[36]
6	RpiL	50S ribosomal protein L7/L12	It is involved in interaction with translation factors	[37]
7	BfrA	Bacterioferritin	It is an intracellular iron storage protein, which protects Mycobacterium from oxidative stress mediated by excess iron	[38]
8	SahH	S-adenosyl-L-homocysteine hydrolase	It is a ubiquitous enzyme that plays a central role in methylation-based processes by maintaining the intracellular balance between S-adenosylhomocysteine (SAH) and S-adenosylmethionine	[39]
9	TrxC	Thioredoxin	It is involved in redox homeostasis and uses it to protect the pathoen against the oxidative intermediates generated by the macrophages	[40]
10	FixB	Electron transfer flavoprotein subunit alpha	It is electron transfer flavoprotein subunit alpha, in some bacteria it functions as nitrogen fixing agent but its function in M .tuberculosis is not clear	[41]
11	PepA	Serine protease	It is a serine protease associated with cell membrane, which stimulates peripheral blood mononuclear cells from healthy PPD donors to proliferate and secrete gamma interferon	[42]
12	Wag31	Hypothetical protein	It is a cell division initiation protein involved in regulation of genes including virulence factors and antigens	[43]
13	Mpt64	Hypothetical protein	It is an immunogenic protein which elicits delayed type hypersensitivity skin response	[44]
14	Apa	Alanine and proline rich secreted protein	It is a cell surface glycoprotein which binds to host lectins and cheat the innate immune system	[45]
15	LprG	Lipoprotein LprG	It plays a role in M. tuberculosis infection by inducing increased suppression of the immune response due to elevated nitric oxide production	[46]
16	Rv1893	Hypothetical protein	Function unknown	[47]
17	Rv1855c	Oxidoreductase	Probable monooxygenase	[48]
18	Gap	Glyceraldehyde-3-phosphate dehydrogenase	It has glyceraldehyde-3-phosphate dehydrogenase activity	[49]