A novel testis‐specific 105‐kDa protein related to the 90‐kDa heat‐shock protein

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Abstract
Brain 90‐ and 100‐kDa heat‐shock proteins (HSP90 and HSP100) were purified and antibodies against them prepared. The two antibodies were very specific and did not cross‐react with each other. In rat, immunoblotting with the anti‐HSP90 antibody showed the most abundant presence of HSP90 in testis as well as brain, compared with lung, liver, spleen, kidney, cardiac muscle, ovarium and uterus. The anti‐HSP90 antibody showed the presence of a new 105‐kDa protein in rat testis. This novel 105‐kDa protein was also detected in brain at a very low concentration but not in HeLa cells or other organs including the uterus and ovarium. The testis 105‐kDa protein was purified from rat testis; although it was clearly separable from HSP90 by two‐dimensional gel electrophoresis, Q‐Sepharose and hydroxyapatite column chromatographies, the properties of this protein were very similar to HSP90. The similarity was higher than 60% on peptide mapping with trypsin digestion, the 105‐kDa protein cross‐reacted with anti‐HSP90 antibody, both were bound similarly to heparin‐Sepharose gel and both are located in the cytosol fraction. When the 105‐kDa protein was fractionated by HPLC, a molecular mass of 195 kDa was calculated, indicating that it is composed of two identical subunits, similarly to HSP90. The 105‐kDa protein did not react with the anti‐HSP100 antibody. There was a slight similarity between the 105‐kDa protein and HSP100 on the peptide mapping. HSP100 was present in the microsomal fraction as well as in the cytosol. It is concluded that the 105‐kDa protein is a testis‐specific and HSP90‐related protein.