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Positive charge in the n-region of the signal peptide contributes to efficient post-translational translocation of small secretory preproteins.

ABSTRACT: Increasing evidence indicates that many small secretory preproteins can undergo post-translational translocation across the membrane of the endoplasmic reticulum. Although the cellular machinery involved in post-translational translocation of small secretory preproteins has begun to be elucidated, the intrinsic signals contained within these small secretory preproteins that contribute to their efficient post-translational translocation remain unknown. Here, we analyzed the eukaryotic secretory proteome and discovered the small secretory preproteins tend to have a higher probability to harbor the positive charge in the n-region of the signal peptide (SP). Eliminating the positive charge of the n-region blocked post-translational translocation of newly synthesized preproteins and selectively impaired translocation efficiency of small secretory preproteins. The pathophysiological significance of the positive charge in the n-region of SP was underscored by recently identified preproinsulin SP mutations that impair translocation of preproinsulin and cause maturity onset diabetes of youth (MODY). Remarkably, we have found that slowing the polypeptide elongation rate of small secretory preproteins could alleviate the translocation defect caused by loss of the n-region positive charge of the signal peptide. Together, these data reveal not only a previously unrecognized role of the n-region's positive charge in ensuring efficient post-translational translocation of small secretory preproteins, but they also highlight the molecular contribution of defects in this process to the pathogenesis of genetic disorders such as MODY.

SUBMITTER: Guo H

PROVIDER: S-EPMC5808753 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Positive charge in the n-region of the signal peptide contributes to efficient post-translational translocation of small secretory preproteins.

Guo Huan H Sun Jinhong J Li Xin X Xiong Yi Y Wang Heting H Shu Hua H Zhu Ruimin R Liu Qi Q Huang Yumeng Y Madley Rachel R Wang Yulun Y Cui Jingqiu J Arvan Peter P Liu Ming M

The Journal of biological chemistry 20171211 6

Increasing evidence indicates that many small secretory preproteins can undergo post-translational translocation across the membrane of the endoplasmic reticulum. Although the cellular machinery involved in post-translational translocation of small secretory preproteins has begun to be elucidated, the intrinsic signals contained within these small secretory preproteins that contribute to their efficient post-translational translocation remain unknown. Here, we analyzed the eukaryotic secretory p ...[more]

PMID: 29229776

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Project description:BackgroundSecretory signal peptides (SPs) are well-known sequence motifs targeting proteins for translocation across the endoplasmic reticulum membrane. After passing through the secretory pathway, most proteins are secreted to the environment. Here, we describe the modification of an expression vector containing the SP from secreted acid phosphatase 1 (SAP1) of Leishmania mexicana for optimized protein expression-secretion in the eukaryotic parasite Leishmania tarentolae with regard to recombinant antibody fragments. For experimental design the online tool SignalP was used, which predicts the presence and location of SPs and their cleavage sites in polypeptides. To evaluate the signal peptide cleavage site as well as changes of expression, SPs were N-terminally linked to single-chain Fragment variables (scFv's). The ability of L. tarentolae to express complex eukaryotic proteins with highly diverse post-translational modifications and its easy bacteria-like handling, makes the parasite a promising expression system for secretory proteins.ResultsWe generated four vectors with different SP-sequence modifications based on in-silico analyses with SignalP in respect to cleavage probability and location, named pLTEX-2 to pLTEX-5. To evaluate their functionality, we cloned four individual scFv-fragments into the vectors and transfected all 16 constructs into L. tarentolae. Independently from the expressed scFv, pLTEX-5 derived constructs showed the highest expression rate, followed by pLTEX-4 and pLTEX-2, whereas only low amounts of protein could be obtained from pLTEX-3 clones, indicating dysfunction of the SP. Next, we analysed the SP cleavage sites by Edman degradation. For pLTEX-2, -4, and -5 derived scFv's, the results corresponded to in-silico predictions, whereas pLTEX-3 derived scFv's contained one additional amino-acid (AA).ConclusionsThe obtained results demonstrate the importance of SP-sequence optimization for efficient expression-secretion of scFv's. We could successfully demonstrate that minor modifications in the AA-sequence in the c-region of the natural SP from SAP1, based on in-silico predictions following the (-3, -1) rule, resulted in different expression-secretion rates of the protein of interest. The yield of scFv production could be improved close to one order of magnitude. Therefore, SP-sequence optimization is a viable option to increase the overall yield of recombinant protein production.

Dataset Information

Positive charge in the n-region of the signal peptide contributes to efficient post-translational translocation of small secretory preproteins.

Publications

Positive charge in the n-region of the signal peptide contributes to efficient post-translational translocation of small secretory preproteins.

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