OVERPRODUCTION AND RAPID PURIFICATION OF HUMAN FAST SKELETAL BETA-TROPONIN-T USING ESCHERICHIA-COLI EXPRESSION VECTORS - FUNCTIONAL DIFFERENCES BETWEEN THE ALPHA-ISOFORM AND BETA-ISOFORM
Ql. Wu et al., OVERPRODUCTION AND RAPID PURIFICATION OF HUMAN FAST SKELETAL BETA-TROPONIN-T USING ESCHERICHIA-COLI EXPRESSION VECTORS - FUNCTIONAL DIFFERENCES BETWEEN THE ALPHA-ISOFORM AND BETA-ISOFORM, Gene, 155(2), 1995, pp. 225-230
Troponin T (TpnT), an essential component of the Ca2+-regulatory tropo
nin complex, is involved in protein-protein interactions with other th
in-filament proteins during muscle contraction in vertebrate striated
muscle (VSM). The isoforms of TpnT are encoded by members of a multige
ne family which, by alternate splicing, produces a complex pattern of
isoproteins in VSM, The functional domains of TpnT are only tentativel
y identified and structure-function analysis on this protein is limite
d due to the heterogeneity of the multiple isoforms. We reasoned that
the overproduction and purification of a single TpnT species in Escher
ichia coli would provide an insight into these studies, besides being
useful in crystallizing the protein. We cloned the human fast skeletal
beta TpnT-encoding cDNA (beta TpnT(f)) in three expression vectors. O
verexpression was achieved in an E. coli BL21(DE3) lysogen using a T7
RNA polymerase promoter-based vector, pET17b. The unfused recombinant
protein was purified by a simple and rapid procedure in a biologically
active and immunoreactive form. This is the first successful synthesi
s of a complete beta TpnT(f) polypeptide from any species using an in
vitro expression system. Purified human beta TpnT(f), a predominant fe
tal form, was less Ca2+-sensitive and exhibited considerably reduced a
ffinity for troponin C and tropomyosin, as compared to the rabbit fast
skeletal alpha TpnT, a predominant adult isoform, These results provi
de a biochemical correlate to the age-related differences in Ca2+ sens
itivity of tension development in vertebrate fast skeletal muscles.