3.6 │ Intrinsic disorder of histone H1 subtypes-interacting
protein complexes
Because transient interactions were frequently presented as coupled to
the protein disorder 48,49,50, it seems advisable to
check in which extend such a phenomena influence on histone H1 subtypes
interactions. In order to found the disordered regions in the interfaces
of physically associated proteins, their sequences were analyzed with
the DisEMBL predictor. For all of the contact regions in the histone H1
subtypes, a characteristic is an occurrence of disordered residues, in
the amount from 50% to 80%. On the other hand, among the histone H1
interacting proteins are six having fully ordered interfaces and six
ones possessing from 83% to 100% of the disordered residues (Figure
5). While histone H1 subtypes were already recognized as abundantly
disordered proteins displaying the representative features of sequence
and structure attributable to the intrinsic structural disorder51, a way of their interactions and a kind of formed
complexes remained unknown. The current analysis allowed to show that
histone H1 subtypes may create two types of complexes via disordered
motifs. According to the categories of complexes introduced by Mészáros
et al. 52, the first encompass interaction between
disordered H1 and ordered partner through the coupled folding and
binding and the second include interaction between disordered H1 and
disordered partner through the mutual synergistic folding. If so,
histone H1 have potential for creation a transient (weaker) interaction
with ordered partner due to the decreasing binding strength evoked by
loss of conformational entropy 53 as well as to form
more stable complexes with disordered partner due to a difference in the
compositions and variation of the backbone sequence.54 A participation of histone H1 in the weaker
interactions results from its intrinsic disorder reaching above 90% of
the sequence, while a share in the stronger ones provides a presence of
MoRFs and APBRs motifs stabilizing the interactions.51 Thus, it seems that a specificity of interaction is
determined by an individual sequence and/or structure properties of the
binding partner. By generalizing, this finding confirm that intrinsic
disorder is an inherent feature of histone H1 subtypes, essential for
recognition and binding of an interacting partner. A disorder-dependent
formation of various complexes seems to be crucial for multifaceted
functioning of histone H1 subtypes.