Lectins have the ability to bind specific carbohydrates and they have potential applications as medical and pharmacological agents. The unique structure and usefulness of red algal lectin have been reported, but these lectins are limited to a few marine algal groups. In this study, a novel mannose-binding lectin from Grateloupia chiangii (G. chiangii lectin, GCL) was purified using antiviral screens and affinity chromatography. We characterized the molecular weight, agglutination activity, hemagglutination activity, and heat stability of GCL. To determine the carbohydrate specificity, a glycan microarray was performed. GCL showed strong binding affinity for Maltohexaose-β-Sp1 and Maltoheptaose-β-Sp1 with weak affinity for other monosaccharides and preferred binding to high-mannan structures. The N-terminal sequence and peptide sequence of GCL were determined using an Edman degradation method and LC-MS/MS, and the cDNA and peptide sequences were deduced. GCL was shown to consist of 231 amino acids (24.9 kDa) and the N-terminus methionine was eliminated after translation. GCL possessed a tandem repeat structure of six domains, similar to the other red algal lectins. The mannose binding properties and tandem repeat structure of GCL may confer it the potential to act as an antiviral agent for protection against viral infection.
Autophagy is a self-degradation system wherein cellular materials are recycled. Although autophagy has been extensively studied in yeast and mammalian systems, integrated stress responses in microalgae remain poorly understood. Accordingly, we carried out a comparative study on the oxidative stress responses of
Chlamydomonas reinhardtii
wild-type and a starchless (
sta6
) mutant previously shown to accumulate high lipid content under adverse conditions. To our surprise, the
sta6
mutant exhibited significantly higher levels of lipid peroxidation in the same growth conditions compared to controls. The
sta6
mutant was more sensitive to oxidative stress induced by H
2
O
2
, whereas the wild-type was relatively more resistant. In addition, significantly up-regulated autophagy-related factors including
ATG1
,
ATG101
, and
ATG8
were maintained in the
sta6
mutant regardless of nitrogen availability. Also, the
sta6
mutant exhibited relatively higher ATG8 protein level compared to wild-type under non-stress condition, and quickly reached a saturation point of autophagy when H
2
O
2
was applied. Our results indicate that, in addition to the impact of carbon allocation, the increased lipid phenotype of the
sta6
mutant may result from alterations in the cellular oxidative state, which in turn activates autophagy to clean up oxidatively damaged components and fuel lipid production.
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