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Escherichia coli Signal Peptidase Recognizes and Cleaves Archaeal Signal Sequence

Majida Atta Muhammad1#, Samia Falak1#, Naeem Rashid1*, Qurra-tul-Ann Afza Gardner1, Nasir Ahmad2, Tadayuki Imanaka3, and Muhammad Akhtar1,4

1University of the Punjab, School of Biological Sciences, 54590 Lahore, Pakistan; E-mail: naeem.ff.sbs@pu.edu.pk, naeemrashid37@hotmail.com

2University of the Punjab, Institute of Agricultural Sciences, 54590 Lahore, Pakistan

3Ritsumeikan University, The Research Organization of Science and Technology, 525-8577 Kusatsu, Shiga, Japan

4University of Southampton, School of Biological Sciences, Southampton SO16 7PX, UK

# These authors contributed equally to this work.

* To whom correspondence should be addressed.

Received March 7, 2017; Revision received April 12, 2017
Tk1884, an open reading frame encoding α-amylase in Thermococcus kodakarensis, was cloned with the native signal sequence and expressed in Escherichia coli. Heterologous gene expression resulted in secretion of the recombinant protein to the extracellular culture medium. Extracellular α-amylase activity gradually increased after induction. Tk1884 was purified from the extracellular medium, and its molecular mass determined by electrospray ionization mass spectrometry indicated the cleavage of a few amino acids. The N-terminal amino acid sequence of the purified Tk1884 was determined, which revealed that the signal peptide was cleaved between Ala26 and Ala27 by E. coli signal peptidase. To the best of our knowledge, this is the first report describing an archaeal signal sequence recognized and cleaved by E. coli signal peptidase.
KEY WORDS: α-amylase, Thermococcus kodakarensis, signal peptide, purification, mass spectrometry, N-terminal sequencing

DOI: 10.1134/S0006297917070070