 formylglycine generating enzyme ( fge ) performs a critical posttranslational modification of type i sulfatases , converting cysteine within the motif cxpxr to the aldehyde - bearing residue formylglycine ( fgly ) . 
 this concise motif can be installed within heterologous proteins as a genetically encoded  
 aldehyde tag  for site - specific labeling with aminooxy- or hydrazide - functionalized probes . in this report , we screened fges from m. tuberculosis and s. coelicolor against synthetic peptide libraries and identified new substrate sequences that diverge from the canonical motif . 
 we found that e. coli s fge - like activity is similarly promiscuous , enabling the use of novel aldehyde tag sequences for in vivo modification of recombinant proteins . 
Supplementary Material