'Venus trapped, Mars transits': Cu and Fe redox chemistry, cellular topography and in situ ligand binding in terrestrial isopod hepatopancreas

作者：Kille P; Morgan A J; Powell K^*; Mosselmans J F W; Hart D; Gunning P; Hayes A; Scarborough D; McDonald I; Charnock J M

来源：Open Biology, 2016, 6(3): 150270.

DOI：10.1098/rsob.150270

• iron
• copper
• speciation
• mu-focus
• synchrotron
• isopod

Woodlice efficiently sequester copper (Cu) in 'cuprosomes' within hepatopancreatic 'S' cells. Binuclear 'B' cells in the hepatopancreas form iron (Fe) deposits; these cells apparently undergo an apocrine secretory diurnal cycle linked to nocturnal feeding. Synchrotron-based mu-focus X-ray spectroscopy undertaken on thin sections was used to characterize the ligands binding Cu and Fe in S and B cells of Oniscus asellus (Isopoda). Main findings were: (i) morphometry confirmed a diurnal B-cell apocrine cycle; (ii) X-ray fluorescence (XRF) mapping indicated that Cu was co-distributed with sulfur (mainly in S cells), and Fe was co-distributed with phosphate (mainly in B cells); (iii) XRF mapping revealed an intimate morphological relationship between the basal regions of adjacent S and B cells; (iv) molecular modelling and Fourier transform analyses indicated that Cu in the reduced Cu+ state is mainly coordinated to thiol-rich ligands (Cu-S bond length 2.3 angstrom) in both cell types, while Fe in the oxidized Fe3+ state is predominantly oxygen coordinated (estimated Fe-O bond length of approx. 2 angstrom), with an outer shell of Fe scatterers at approximately 3.05 angstrom; and (v) no significant differences occur in Cu or Fe speciation at key nodes in the apocrine cycle. Findings imply that S and B cells form integrated unit-pairs; a functional role for secretions from these cellular units in the digestion of recalcitrant dietary components is hypothesized.

• 出版日期2016-3