Received January 6, 2006
Returned for revision February 24, 2006
Accepted April 17, 2006
Lentinula edodes tlg1 encodes a thaumatin-like protein that is involved in lentinan degradation and fruiting body senescence
Yuichi Sakamoto *, Hisayuki Watanabe , Masaru Nagai , Keiko Nakade , Machiko Takahashi , and Toshitsugu Sato
Iwate Biotechnology Research Center, 22-174-4 Narita, Kitakami-shi, Iwate, 024-0003, Japan
* Corresponding author; email: sakamoto{at}ibrc.or.jp.
Lentinan is an anti-tumor product that is purified from fresh Lentinula edodes fruiting bodies. It is a cell wall component, comprising 
-1,3-glucan with -1,6-linked branches, which becomes degraded during post-harvest preservation as a result of increased glucanase activity. In this study, we used N-terminal amino acid sequence to isolate tlg1, a gene encoding a thaumatin like (TL) protein in L. edodes. The cDNA clone was approximately 1.0 kbp, whereas the genomic sequence was 2.1 kbp and comparison of the two indicated that tlg1 contains 12 introns. The tlg1 gene product (TLG1) was predicted to comprise 240 amino acids, with a molecular weight of 25 kD and pI value of 3.5. The putative amino acid sequence exhibits approximately 40 % identity with plant TL-proteins, and fungal genome databases search revealed that these TL-proteins are conserved in many fungi including the basidiomycota and ascomycota. Transcription of tlg1 was not detected in vegetative mycelium or young and fresh mushrooms. However, transcription increased following harvest. Western blot analysis demonstrated a rise in TLG1 levels following harvest and spore diffusion. TLG1 expressed in E.coli and Aspergillus oryzae exhibited -1,3-glucanase activity, and when purified from the L. edodes fruiting body, demonstrated lentinan degrading activity. Thus we suggest that TLG1 is involved in lentinan and cell wall degradation during senescence following harvest and spore diffusion.
