Abstract
Cadmium (Cd) pollution in cultivated land is caused by irresistible geological factors and human activities; intense diffusion and migration have seriously affected the safety of food crops. Plants have evolved mechanisms to control excessive influx of Cd in the environment, such as directional transport, chelation and detoxification. This is done by some specific metalloproteins, whose key amino acid motifs have been investigated by scientists one by one. The application of powerful cell biology, crystal structure science, and molecular probe targeted labeling technology has identified a series of protein families involved in the influx, transport and detoxification of the heavy metal Cd. This review summarizes them as influx proteins (NRAMP, ZIP), chelating proteins (MT, PDF), vacuolar proteins (CAX, ABCC, MTP), long-distance transport proteins (OPT, HMA) and efflux proteins (PCR, ABCG). We selected representative proteins from each family, and compared their amino acid sequence, motif structure, subcellular location, tissue specific distribution and other characteristics of differences and common points, so as to summarize the key residues of the Cd binding target. Then, we explain its special mechanism of action from the molecular structure. In conclusion, this review is expected to provide a reference for the exploration of key amino acid targets of Cd, and lay a foundation for the intelligent design and breeding of crops with high/low Cd accumulation.
Highlights
Cd is a naturally occurring environmental toxicant, which is absorbed and accumulated by plants, and has strong teratogenic and mutagenic effects on organisms
The members of the natural resistance-associated macrophage protein (NRAMP), ZRT, IRT-like protein (ZIP), metallothionein (MT) and plant defensins (PDF), cation/proton exchanger (CAX), ATP-binding cassette transporters (ABC), metal tolerance protein/cation diffusion facilitator (MTP/CDF), heavy metal ATPase (HMA), oligopeptide transporter (OPT) and plant Cd resistance (PCR) families are closely related to the influx, chelation, transport and efflux of Cd in plants
The DPGN residue near TMD1 was identified as the binding site of the NRAMP transporter (Figure S1), which coordinates with divalent metal ions and participates in the transport of Cd to plant root cells [29]
Summary
Cd is a naturally occurring environmental toxicant, which is absorbed and accumulated by plants, and has strong teratogenic and mutagenic effects on organisms. By integrating the data in http://ipf.sustech.edu.cn/pub/ athrna/ (accessed on 30 December 2021), it was found that ABA, JA, SA hormones are closely related to the expression of cadmium transport and detoxification genes (Figure 1). A BNriRefAIMntPro, daucptrioontonto-ctohuepNleRdAmMePtalFaiomniltyr,atnhsepKoretyerP, riosteainnsaRnceileantetdintotaCctdmIneflmubxraanned the Metcrhaannsipsomrtoefr Afacmtiiolny It is widely present in bacteria, fungi, plants and animals, and participaNteRs AinMthPe, tarapnrsoptoornta-ctioounpolfeda vmareiteatlyioofndtirvaanlesnptomrteetra,lisioanns [a2n7c].ieUnstiningtoanctlimneesmofbtwraanre transpor(thetrtpf:a//mwlialyb.etIhtzi.cshw/pirdotetleyr/sptarerts/e) n(atccinessbeadctoenri3aF, efburnugari,y p20la2n2)tstoamndapatnhiemir atrlasn, samnedmp- articipatbersainne tdhoemtraainnssp(ToMrtDatsi)oannodfaamvinaorieatcyidosftrduicvtaulreanl tfemateutraelsio[2n8s],[i2t7w].aUs sfoinugndonthliant ethseoyftware (http://wlab.ethz.ch/protter/start/) (accessed on 30 December 2021) to map their transmembrane domains (TMDs) and amino acid structural features [28], it was found that they typically have 12 TMDs. The DPGN residue near TMD1 was identified as the binding site of the NRAMP transporter (Figure S1), which coordinates with divalent metal ions and participates in the transport of Cd to plant root cells [29]. The mutations of histidine in AtNRAMP3 severely impaired the transport of Fe and Mn, and partially impaired the transport of Cd [35]
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