  We extract polarized parton distribution functions (PPDFs), referred to as
"KTA17," together with the highly correlated strong coupling $\alpha_s$ from
recent and up-to-date $g_1$ and $g_2$ polarized structure functions world data
at next-to-next-to-leading order in perturbative QCD. The stability and
reliability of the results are ensured by including nonperturbative target mass
corrections as well as higher-twist terms which are particularly important at
the large-$x$ region at low Q$^2$. Their role in extracting the PPDFs in the
nucleon is studied. Sum rules are discussed and compared with other results
from the literature. This analysis is made by means of the Jacobi polynomials
expansion technique to the DGLAP evolution. The uncertainties on the
observables and on the PPDFs throughout this paper are computed using standard
Hessian error propagation which served to provide a more realistic estimate of
the PPDFs uncertainties.
