Background: The unique hypervariable C-terminal region (HVR) of K-Ras4B, one of
the most frequently mutated proteins in many powerful cancers, contains a C-terminal farnesylated
and methylated Cys and a poly-lysine motif, which decides the association of K-Ras4B to the inner
leaflet of plasma membrane for activating the downstream signaling activity. In our previous work,
we inserted an additional Cys in K-Ras4B HVR peptide synthesis for NCL in the semi-synthesis of
K-Ras4b protein, but it is not suitable for application in protein dimerization research. The recently
developed selenocysteine (Sec, U) mediated native chemical ligation reaction followed by selective
deselenization, which can help to broaden the scope of protein synthesis, requires the generation of
the peptide fragment with an N-terminal Sec.
Objective: To synthesize K-Ras4B HVR peptide containing both N-terminal Sec and C-terminal
farnesylated and methylated Cys to achieve traceless protein semi-synthesis.
Methods and Results: We have developed a facile synthesis approach for producing Boc-Sec)2-OH
using economic Se powder, which can facilitate scaling up preparation of peptides containing Sec
at the N-terminus. Furthermore, we synthesized K-Ras4B HVR peptide containing selenocystine
by utilization of Boc-Sec)2-OH. Finally, we took K-Ras4B HVR peptide as an example to test the
compatibility of farnesylation reaction at Cys with the N-terminal Sec)2, and the farnesyl group
was successfully added to the thiol group of Cys.