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. 2017 Nov 3;7:14499. doi: 10.1038/s41598-017-14833-8

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© The Author(s) 2017

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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LC-MS analysis reveals signal peptide cleavage homogeneity of recombinant IGF1 expressed with an amino-terminal bombyxin signal peptide in the presence of reducing agent TCEP. (a) Reduced IGF1 eluted later than the non-reduced form in the total ion chromatogram. Single charged background ions with high intensity representing masses < 1 kDa are marked with asterisks. (b) The proteomic spectrum corresponding to the peak at 13.6–14.1 min with 27 averaged scans displayed several characteristic mass-to-charge ratio peaks. (c) The transformed, deconvoluted mass spectrum of recombinant reduced IGF1 displayed several peaks at 9155.2, 9171.9, 9186.8 and 9283.4 amu representing molecular masses of IGF1 with different structures. Minor peaks that do not match molecular masses of any cleavage forms of IGF1 could represent contaminants detected in purified IGF1 (see Fig. 1c). Detected cleavage site is indicated by a red line in the upper right sequence of the signal peptide – IGF1 junction.