Duplication and divergence of the amino-terminal coding region of the complement receptor 1 (CR1) gene. An example of concerted (horizontal) evolution within a gene.

Abstract Complement activation on human platelets is known to cause platelet degranulation and activation. To evaluate how normal platelets escape complement attack in vivo, we studied the fate of murine platelets deficient in 2 membrane complement regulatory proteins using an adoptive transfer model. We show here that deficiency of either decay-accelerating factor (DAF) or complement receptor 1–related gene/protein y (Crry) on murine platelets was inconsequential, whereas DAF and Crry double deficiency led to rapid clearance of platelets from circu-lation in a complement- and macrophage-dependent manner. This finding contrasted with the observation on erythrocytes, where Crry deficiency alone resulted in complement susceptibility. Quantitative flow cytometry revealed that DAF and Crry were expressed at similar levels on platelets, whereas Crry expression was 3 times higher than DAF on erythrocytes. Antibody blocking or gene ablation of the newly identified complement receptor CRIg, but not complement receptor 3 (CR3), rescued DAF/Crry-deficient platelets from complement-dependent elimination. Surprisingly, deficiency of CRIg, CR3, and other known complement receptors failed to prevent Crry-deficient erythrocytes from complement-mediated clearance. These results show a critical but redundant role of DAF and Crry in platelet survival and suggest that complement-opsonized platelets and erythrocytes engage different complement receptors on tissue macrophages in vivo.

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Signal peptide specificity in posttranslational processing of the plant protein phaseolin in Saccharomyces cerevisiae.

Molecular and Cellular Biology ◽

10.1128/mcb.7.1.121 ◽

1987 ◽

Vol 7 (1) ◽

pp. 121-128 ◽

Cited By ~ 15

Author(s):

J H Cramer ◽

K Lea ◽

M D Schaber ◽

R A Kramer

Keyword(s):

Saccharomyces Cerevisiae ◽

Acid Phosphatase ◽

Signal Peptide ◽

Regulatory Region ◽

Cellular Protein ◽

Proteolytic Processing ◽

Coding Region ◽

Molecular Weights ◽

Amino Terminal ◽

Acid Phosphatase Gene

We linked the cDNA coding region for the bean storage protein phaseolin to the promoter and regulatory region of the Saccharomyces cerevisiae repressible acid phosphatase gene (PHO5) in multicopy expression plasmids. Yeast transformants containing these plasmids expressed phaseolin at levels up to 3% of the total soluble cellular protein. Phaseolin polypeptides in S. cerevisiae were glycosylated, and their molecular weights suggested that the signal peptide had been processed. We also constructed a series of plasmids in which the phaseolin signal-peptide-coding region was either removed or replaced with increasing amounts of the amino-terminal coding region for acid phosphatase. Phaseolin polypeptides with no signal peptide were not posttranslationally modified in S. cerevisiae. Partial or complete substitution of the phaseolin signal peptide with that from acid phosphatase dramatically inhibited both signal peptide processing and glycosylation, suggesting that some specific feature of the phaseolin signal amino acid sequence was required for these modifications to occur. Larger hybrid proteins that included approximately one-half of the acid phosphatase sequence linked to the amino terminus of the mature phaseolin polypeptide did undergo proteolytic processing and glycosylation. However, these polypeptides were cleaved at several sites that are not normally used in the unaltered acid phosphatase protein.

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