1 │ INTRODUCTION
Usually, protein exert its biological function forming a pair with other
protein as a result of interaction. Due to a great diversity of
variously created protein complexes, the protein-protein interactions
might be defined in several contexts. They are direct when proteins stay
in close, physical, contact with other protein or indirect when
interaction between proteins is maintained by intermediate in the
complex. 1 In respect of a stability, protein-protein
interaction might be stable and irreversible, i.e. permanent, or able to
temporal association/dissociation, i.e. transient. In terms of binding
affinity, the permanent interactions are usually obligate, i.e.
including components that cannot exist independently, while transient
are non-obligate, i.e. including constituents able to exist
independently. 2 Irrespective of the constituents of
interactions and a type of created complexes, the interactions between
proteins are crucial for a right course of all cellular processes
running in the various cellular structures. 3 One of
them is chromatin, a multi-subunit complex contained over 1900 proteins
participating in DNA templated processes, such as gene regulation,
packaging and repair. 4 In chromatin, a highly
abundant are histones. They represent five classes of proteins, i.e.
H2A, H2B, H3, H4 and H1, responsible for organization of chromatin
structure and modulation of its genetic and epigenetic functioning.5
Histone H1 is well-known as core component of chromatin implicated in
maintenance of nucleosomal and linker DNA to promote chromatin
compaction and formation of its higher order structure.6,7 Such canonical account of histone H1 functioning
is nowadays supplemented by its activity realized through the
interactions with proteins that differ in their cellular localization
and belongs to distinct functional categories. They include
spliceosome-associated proteins, core histone binding chaperone
proteins, regulatory transcription proteins, DNA damage repair proteins
and translation-associated proteins. 8 Thus, histone
H1 extended paradigm point that it should be seen as multifunctional
protein engaged in the course of diverse biological processes. However,
a vast majority of known histone H1 partnering proteins refers to the
one human histone H1 subtype, i.e. H1.0. To know a broader range of
histone H1 activities realized via interaction with partner proteins, a
successive analyzes concerning subsequent histone H1 subtypes are
needed. This work is aimed at fill this gap through the characteristic
of proteins that interact with five standard human histone H1 somatic
subtypes (H1.1 – H1.5). To do this, the identification of histone H1
partnering proteins subcellular localization was performed together with
prediction of their molecular function and biological processes.
Besides, the histone H1 interaction networks were constructed to show a
scope of their activity. Based on the secondary structure motifs and
amino acid composition of proteins binding interfaces, a strength of
protein-protein interaction and a type of formed complexes was
appointed. Finally, an impact of intrinsic structural disorder on
protein-protein interaction was determined to define a mechanism of
protein complex formation. A scheme depicting the data processing stages
is presented in the Fig.1.