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Table 2 Main protein candidates for serodiagnosis that have been cross-validated by proteomic studies

From: Proteomics paves the way for Q fever diagnostics

Protein (locus-tag)

Identification

MW (kDa)

pI

Protein function

Nature of protein

Peptide signal sequence

Nature of analyzed samples

DT

Clinical significance

Reference(s)

CBU_0952

Acute disease antigen A (adaA)

25.9

8.67

Unknown

Membrane

MKKLTVTFLTFISIFFAATAAFA

Cb isolates

BT, IP

Marker of acute Q fever

[31, 63]

CBU_0612

Putative outer membrane chaperone protein (ompH, Skp)

18.8

9.71

Molecular chaperone, interacts with unfolded proteins

Membrane*

MIKRLLSAICLSVAMIWSVAAVAQTVGLVD

Patient sera, Cb NM II TPE

IP, RP

Marker of Q fever endocarditis, SP with Q fever patients (general)

[56, 57]

CBU_0937

Hypothetical protein

51.4

8.99

Unknown

Membrane

MTSKLVISALGLCVSGALSTTLAST

mAbs, Cb NM II TPE, RP-based ELISA/HS

IP, BT

Marker of Q fever endocarditis. Marker of phase II

[17, 56, 58]

CBU_1910

Outer membrane protein (com1)

27.6

9.08

Protein disulfide oxidoreductase, unknown role in pathogenesis

Membrane

MKNRLTALFLAGTLTAGVAIAAPSQF

mAbs, Cb NM II TPE

IP, BT, RP

SP with both acute Q fever and Q fever endocarditis. Marker of both phase I and phase II

[17, 58, 65, 67–69]

CBU_0236

Elongation factor Tu (tuf-2)

43.5

5.32

GTP-dependent binding of aminoacyl-tRNA in protein biosynthesis

Soluble*†

 

mAbs, TPE Cb NM II, HS, AS (infected/vaccinated guinea pigs)

IP

SP, marker of acute Q fever

[31, 58, 65, 68]

CBU_0092

Tol-pal system protein (YbgF)

34.3

6.46

Critical for maintaining integrity of bacterial outer membrane Involved in protein-protein interactions

Membrane

MRLIKMKIKTLCVSSALAALMLSAPLTWADA

TPE Cb NM I and II HS Q-fever (general), AS (immunized guinea pigs) protein microarray

IP, RP

Phase II-specific marker (early diagnosis of acute Q fever), marker of Q fever (general)

[68, 69]

CBU_0311

Outer membrane porin (Coxiella porin P1)

26.8

8.44

Able to form pore in lipid bilayers

Membrane*† OM location shown for Cb NM I

METTTKLAIGVSALCCLASAAFAGGPD

ELISA and ELISPOT based on RP/AS IP: HS, and AS (infected/vaccinated guinea pigs)

RP, IP

Marker of Q fever (general), marker of acute Q fever; applications for drug and vaccine development

[31, 67]

CBU_1718

Chaperonin (GroL)

58.284

5.14

Protein folding, ATP hydrolysis

Soluble†

 

HS/TPE Cb NM II/RP; IP HS, and AS (infected/vaccinated guinea pigs)

IP, RP

Marker of Q fever (general), marker of acute Q fever

[31, 65]

CBU_0229

50S ribosomal protein L7/L12 (RplJ)

13.2

4.71

Binding site for several factors in protein synthesis

Membrane†

MAQLSKDDILEAVANMSVMDVVDLVKAMEEKFGVSAQAAIAVAGPVAGGEA

IP: HS, and AS (infected/vaccinated guinea pigs)

BT, IP

Marker of both phase I and phase II, marker of acute Q fever

[17, 31]

CBU_0263

DNA-directed RNA polymerase subunit alpha (rpoA)

35.5

5.61

DNA-dependent RNA polymerase transcription

Soluble

 

OMP fraction of Cb NM II and CbuG_Q212 II; Phase 1 HS (chronic )

IP

Marker of chronic Q fever

[2, 69]

CBU_1916

Universal stress protein family

15.78

6.58

Stress response

Soluble*

 

OMP fraction of Cb NM II and CbuG_Q212 II; Phase 1 HS (chronic)

IP

Marker of chronic Q fever

[1, 69]

  1. I, phase I; II, phase II; AS, animal sera; BT, biotyping; Cb, Coxiella burnetii; DT, discovery technology; HS, human sera; IP, immunoproteomics; mAb, monoclonal antibody; MW, molecular weight; NM, Nine Mile; OM, outer membrane; OMP, outer membrane protein; pI, isoelectric point; RP, recombinant protein-based approaches; SP, seroreactive proteins; TPE, total protein extract.
  2. Soluble (cytosolic). Membrane (having a signal peptide that directs protein to the cell membrane). *More than two-fold more abundant in the LCV stage than in the SCV stage. †Proteins common to SCV and LCV.