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[Preprint]. 2023 Sep 17:2023.09.17.558117. [Version 1] doi: 10.1101/2023.09.17.558117

Fig. 2: Architecture of the catalytically active SPARTA oligomer.

Fig. 2:

(a) The cryo-EM map shows the domain organization of the “butterfly” shaped SPARTA oligomer with gRNA/tDNA. The oligomer is organized as a tetramer of heterodimers (labeled as A, B, C and D). The TIR, APAZ, short pAgo (MID-PIWI) are shown in yellow, green and blue, respectively. The connector between the TIR and APAZ domain is shown in pink and the gRNA/tDNA is depicted in red. This composite cryo-EM map was obtained by using C2 based focused symmetry refinement of both ‘wings’ and local refinement of TIR domains. (b) Structural arrangement of the SPARTA oligomer. The protein and nucleic acid components are colored as in (a). Dimensions of the complex are given in Å. (c) Structural comparison of the tetrameric arrangement of TIR domain assembly in SPARTA oligomer versus that in select proteins with scaffolding (MAL) and enzymatic (AbTir and SARM1) roles. The secondary structure elements are labeled for SPARTA TIR. AbTir and SARM1 are depicted with bound NAD+ analogue (shown in sticks).