9.B.111 The 6TMS Lysyl tRNA synthetase (LysS) Family
Several lysyl tRNA synthetases include a 6 TMS segment that appears to correspond to the second 6 TMS unit in certain MFS permeases of the DHA2 family (2.A.1.3). Two such proteins from Streptomyces coelicolor (O69916 and Q9X8H7) show sequence similarity to the proteobacterial MFS permease, E5Y3Y1 (TC#2.A.1.3.47) from Bilophila wadsworthia, a putative 13 TMS protein. The regions of sequence similarity are TMSs 2-5 in the former protein aligning with TMSs 2-5 in the second half of the latter protein. This hydrophobic second 6 TMS units in the domain in LysS may have derived from the second half of an MFS permease. It is not known if it has transport function. However, two proteins in the MFS (2.A.1.3.37 and 2.A.1.3.44) have the lysyl tRNA synthetase domain C-terminal to the MFS domain. These results need to be confirmed.