Table 1 Functional classification of proteins common in all PPDs

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]