Conformational plasticity and evolutionary analysis of the myotilin tandem Ig domains

Vid Puž,Kristina Djinović-Carugo,Brigita Lenarčič,Miha Pavšič

doi:10.1038/s41598-017-03323-6

Vid Puž, Kristina Djinović-Carugo + Show 2 more

Open Access

https://doi.org/10.1038/s41598-017-03323-6

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Abstract

Myotilin is a component of the sarcomere where it plays an important role in organisation and maintenance of Z-disk integrity. This involves direct binding to F-actin and filamin C, a function mediated by its Ig domain pair. While the structures of these two individual domains are known, information about their relative orientation and flexibility remains limited. We set on to characterise the Ig domain pair of myotilin with emphasis on its molecular structure, dynamics and phylogeny. First, sequence conservation analysis of myotilin shed light on the molecular basis of myotilinopathies and revealed several motifs in Ig domains found also in I-band proteins. In particular, a highly conserved Glu344 mapping to Ig domain linker, was identified as a critical component of the inter-domain hinge mechanism. Next, SAXS and molecular dynamics revealed that Ig domain pair exists as a multi-conformation species with dynamic exchange between extended and compact orientations. Mutation of AKE motif to AAA further confirmed its impact on inter-domain flexibility. We hypothesise that the conformational plasticity of the Ig domain pair in its unbound form is part of the binding partner recognition mechanism.

Highlights

Movement is vital to all living organisms, from the transport of single molecules in cells to the movement of the entire organism
Myotilin is comprised of two C2-type Ig domains and a unique serine-rich N-terminal region[4], while palladin and myopalladin host up to five Ig domains, where the two most C-terminal domains share high homology with the Ig domains of myotilin and two most N-terminal domains are mostly related to the N2B region of titin[5] (Fig. 1a)
Via canonical motif 1-4-5-8 myotilin is able to interact with EF3-4 hands of α-actinin, in a similar way as it was shown for titin Z-repeats[14,15,16,17], palladin[13, 18] and more recently for neck peptide of α-actinin-2 in its auto-inhibited form[19]

Summary

Introduction

Movement is vital to all living organisms, from the transport of single molecules in cells to the movement of the entire organism. Titin and nebulin (and its smaller cardiac variant nebulette) act as a general blueprint for sarcomere assembly and length, due to their outstanding size and modular architecture. Sarcomere is on both ends delimited with Z-discs, which act as passive transducers of the generated tension. This is the spot of actin filament crosslinking, primarily by the α-actinin, other signalling, stretch-sensing and actin-binding proteins are involved, for example myotilin, filamin C, ZASP/cypher/oracle, FATZ/myozenin/calsarcin and many others[3]. The founding member of the myotilin/myopalladin/palladin family was initially identified and characterised as α-actinin binding protein[4]. Recent results reported that it is highly mobile in the Z-bodies and in the Z-bands and possesses ability of dynamic exchange with the cytoplasmic pool of proteins, indicating important role in initial organisation and maintenance of Z-disc[22]

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