The uptake and anterograde axonal transport of ' 25 1-wheat germ agglutinin (WGA) has been investigated in the visual system of the chick . In order to obtain a marker with specific and homogeneous binding properties, the iodinated lectin was affinity purified by passage over an Nacetylglucosamine (NAcGlu)-Sepharose column after iodination . 22 h after vitreal injection of the purified ' 25 1-WGA, radioactive label was found accumulated in the retinoreceptive layers of the contralateral optic tectum. Gel electrophoresis of tectal homogenates revealed that > 80% of the retrieved label ran in a band which comigrated with native WGA . In chicks injected with the fraction of the iodinated preparation that failed to bind to the affinity column, there was no evidence of tectal labeling . These findings support the hypothesis that WGA is selectively taken up by chick retinal ganglion cells and transported intact in an anterograde direction to their axon terminals in the contralateral optic tectum. This raises the possibility that constituents of perikaryal membrane, i .e ., lectin receptors, are transported in an anterograde direction by chick retinal ganglion cells .

Living organisms use a large panel of mechanisms to protect themselves from environmental stress.Particularly, heat stress induces misfolding and aggregation of proteins which are guarded by chaperone systems. Here, we examine the function the glutaredoxin GRXS17, a member of thiol reductases families in the model plant Arabidopsis thaliana. GRXS17 is a nucleocytosolic 30 monothiol glutaredoxin consisting of an N-terminal thioredoxin (TRX)-domain and three CGFSactive site motif-containing GRX-domains that coordinate three iron-sulfur (Fe-S) clusters in a glutathione (GSH)-dependent manner. As a Fe-S cluster-charged holoenzyme, GRXS17 is likely involved in the maturation of cytosolic and nuclear Fe-S proteins. In addition to its role in cluster biogenesis, we showed that GRXS17 presents both foldase and redox-dependent holdase activities. 35Oxidative stress in combination with heat stress induces loss of its Fe-S clusters followed by subsequent formation of disulfide bonds between conserved active site cysteines in the corresponding TRX domains. This oxidation leads to a shift of GRXS17 to a high-MW complex and thus, activates its holdase activity. Moreover, we demonstrate that GRXS17 is specifically involved in plant tolerance to moderate high temperature and protects root meristematic cells from 40 heat-induced cell death. Finally, we showed that upon heat stress, GRXS17 changes its client proteins, possibly to protect them from heat injuries. Therefore, we propose that the iron-sulfur cluster enzyme glutaredoxin GRXS17 is an essential guard to protect proteins against moderate heat stress, likely through a redox-dependent chaperone activity. All in all, we reveal the mechanism of an Fe-S cluster-dependent activity shift, turning the holoenzyme GRXS17 into a holdase that 45 prevents damage caused by heat stress.