  Understanding how proteins fold into their native structure is a fundamental
problem in biophysics, crucial for protein design. It has been hypothesized
that the formation of a molten globule intermediate precedes folding to the
native conformation of globular proteins; however, its thermodynamic properties
are poorly known. We perform single-molecule pulling experiments of protein
barnase in the range of 7$^\circ$C to 37$^\circ$C using a temperature-jump
optical trap. We derive the folding free energy, entropy and enthalpy, and heat
capacity change ($\Delta C_p = 1050\pm50$ cal/mol$\cdot$K) at low ionic
strength conditions. From the measured unfolding and folding kinetic rates, we
also determine the thermodynamic properties of the transition state, finding a
significant change in $\Delta C_p$ ($\sim$ 90$\%$) between the unfolded and the
transition states. In contrast, the major change in enthalpy ($\sim$ 80$\%$)
occurs between the transition and native states. These results highlight a
transition state of high energy and low configurational entropy structurally
similar to the native state, in agreement with the molten globule hypothesis.
