Secretion signal sequence

Sletta, H., Aune, R., Nedal, A. etal. (2007) The presence of N-terminal secretion signal sequences leads to strong stimulation of the total expression levels of three tested medically important proteins during high-cell-density cultivations of Pichia pastoris. Applied and Environmental Microbiology, 73 (3), 906-912. 

Current strategies to improve productivity and secretion efficiency comprise (1) enhancement of gene expression rates, (2) optimization of secretion signal sequences, (3) coexpression of chaperones and foldases, (4) creation of protease deficient mutants to avoid premature product degradation, and (5) subsequent breeding and mutagenesis. 

CNTF is expressed in glial cells within the central and peripheral nervous system. CNTF lacks a signal sequence and is not secreted by the classical secretory pathway, but is thought to convey its cytoprotective effects after release from adult glial cells by some mechanism induced by injury [3,5]. 

Up to now, the pectinolytic enzymes of E. chrysanthemi that have been detected were extracellular secreted enzymes (PelA, B, C, D, E, L, exo-Peh and PemA), periplasmic (exo-Pel), or cytoplasmic (OGL) proteins (1, 5). In contrast, PemB is an outer membrane pectinolytic enzyme. To our knowledge it is the first pectinase characterised as a membrane protein. We presented several lines of evidence showing that PemB is a lipoprotein (i) Its N-terminal sequence has the characteristics of lipoprotein signal sequences, (ii) PemB is synthesised as a high molecular weight precursor processed into a lower molecular weight mature form, (iii) Palmitate, the most prevalent fatty acid in bacterial lipoproteins (12), is incorporated into PemB. 

Tashiro K, Tada H, Heilker R, Shirozu M, Nakano T, Honjo T. Signal sequence trap a cloning strategy for secreted proteins and type I membrane proteins. Science 1993 261 600-603. 

The published filarial chitinases show a distinct modular domain structure (Fig. 10.3). The first 17-22 amino acids serve as a cleavable signal sequence, indicating that the enzymes are secreted or are components of the outer membrane. The catalytic domain, essential for the degradation of... 

The presence of foreign protein in the medium of plant cultures does not necessarily mean that all or even most of the product can be recovered from the medium. In many expression systems where an appropriate signal sequence has been used, considerable amounts of foreign protein remain within the plant cells and/or tissues. For example, in a comparison of IgG antibody production in tobacco cell suspension and hairy root cultures, a maximum of 72% of the total antibody was found in the medium of the suspension cultures whereas only 26% was found in the medium of the hairy root cultures [17]. This result could indicate that secretion and/or transport across the cell wall was slower in the hairy roots alternatively, it could indicate poorer stability of the secreted protein in the hairy root medium. If foreign proteins are to be purified from the medium, improved secretion and extracellular product stability are desirable. 

Protein targetii Secreted or membrane proteins N-terminal hydrophobic signal sequence... 

Answer B. Decreased Factor V secretion and a corresponding accumulation of cytoplasmic antigen suggest a defect in the translocation of the nascent protein to the endoplasmic reticulum. This implies a mutation in the N-terminal amino acid signal sequence required for targeting to the ER and encoded by the first exon of the gene. 

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