A novel extracellular Mn-superoxide dismutase (SOD) was isolated from a moss, Barbula unguiculata. The SOD was a glycoprotein; the apparent molecular mass of its native form was 120 kDa, as estimated by gel filtration chromatography, and that of its monomer was 22,072 Da, as estimated by time of flight mass spectroscopy. The protein had manganese with a stoichiometry of 0.80 Mn/monomer. The cDNA clone for a gene encoding the extracellular Mn-SOD was isolated. Sequence analysis showed that it has a strong similarity to germin (oxalate oxidase) and germin-like proteins (GLPs) of several plant species and possesses all the characteristic features of members of the germin family. The clone encoding this extracellular Mn-SOD was therefore designated B. unguiculata GLP (BuGLP). BuGLP had no oxalate oxidase activity. In addition, the cDNA for a gene encoding the moss mitochondrial Mn-SOD was isolated. Its amino acid sequence had little similarity to that of BuGLP, even though a close similarity was observed among the mitochondrial Mn-SODs of various organisms. BuGLP was the first germin-like protein that was really demonstrated to be a metalloprotein with Mn-SOD activity but no oxalate oxidase activity.

;To estimate the physiological roles of a germin-like protein (BuGLP) with Mn-SOD activity isolated newly from a moss, Barbula unguiculata, BuGLP mRNA levels during cell growth and the effects of methyl viologen and salt stress were studied. BuGLP mRNA levels were at their peak during the exponential phase of growth and decreased thereafter, but SOD activity was held at the same level as that during the exponential phase. When methyl viologen was present as a generator of superoxide the amount of BuGLP transcripts decreased, but that of SOD activity of BuGLP bound to the cell wall was not affected. The addition of NaCl to the cells during the logarithmic phase increased both the BuGLP mRNA levels and total SOD activity of BuGLP, but decreased the SOD activity bound to the cell wall due to release of most of the SOD activity into the medium. On the other hand, the addition of NaCl to the cells during the stationary phase hardly affected BuGLP mRNA levels or SOD activity levels bound to the cell wall. These results suggest that the induction of BuGLP gene by salt stress is caused by dissociation of BuGLP protein from the cell wall into the medium in the cells during the logarithmic phase.

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