Structural classification of mycobacterial Ldts (Msm, M. smegmatis; Mtb, M. tuberculosis). Schematic protein organization of each class of mycobacterial Ldts is shown, derived from analyses of the translated sequences of the Ldt genes in 18 mycobacterial genomes. The proteins can be grouped into six classes. Class 5 and 2 are lipoproteins (Lipobox) and also contain a PRR C terminus. Class 1 proteins contain a conserved Region 1 sequence, whilst class 3 and class 6 share a conserved Region 2 sequence along with the Region 1 sequence. Class 6 proteins also have an internal PRR sequence. Class 4 proteins have a conserved PRR sequence in the N terminus. Black boxes at the N termini of some of the proteins indicate predicted transmembrane helices according to genome annotation. All classes contain the characteristic active-site region, HXX14–17[S/T]HGChN (where h is a hydrophobic residue), containing the catalytic cysteine residues. Note that two residues preceding the cysteine, only class 5 has an asparagine instead of the conserved histidine.