**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Name: Sarita Puri
Institution: Department of Bioscience, University of Milan, Italy.
City: Milan
State: Lombardy, Italy.

**Main Body of the Abstract**
This study extensively characterizes full-length (FL) and isolated domains; variable (VL) and constant (CL) of a patient-derived λ-light chain (LC) named AL55 whose fibril structures from the heart and kidney deposits were solved by our work, to unravel the factors influencing its amyloidogenic behavior. The X-ray structure of FL AL55 and data from hydrogen-deuterium exchange mass spectrometry unveil an open conformation of the two VLs in the dimeric structure, featuring a highly dynamic interface distinct from closed conformations observed in other known toxic LCs. This open structure enhances the VL’s susceptibility to proteolytic digestion, potentially facilitating amyloid formation from the isolated VL domain. Investigation into isolated domains confirms that the isolated VL is less structured, unstable, and dynamic in the CDR1 and CDR2 regions, correlating with its higher aggregation under in-vitro conditions. Additionally, unfolding and refolding kinetic experiments provide in-depth insight into the slow unfolding rates of FL and CL but the fast unfolding rate of VL which confirms the rate-limiting step in FL unfolding is stable CL domain. However, limited refolding due to the slow refolding rate of the VL domain confirms a shift of folding transition towards a misfolded conformation which might favor aggregation. Cytotoxicity assay in C. elegans shows soluble toxicity of FL AL55. Additionally, highly polymorphic amyloid fibrils formed by VL show that in-vitro formed fibrils are not truly representative of in-vivo deposited fibrils. Collectively, this research yields crucial insights into the structural and biophysical features influencing AL55 amyloidogenic behavior, presenting potential avenues for therapeutic intervention.



**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Name: Sarita Puri
Institution: Department of Bioscience, University of Milan, Italy.
City: Milan
State: Lombardy, Italy.

**Main Body of the Abstract**
This study extensively characterizes full-length (FL) and isolated domains; variable (VL) and constant (CL) of a patient-derived λ-light chain (LC) named AL55 whose fibril structures from the heart and kidney deposits were solved by our work, to unravel the factors influencing its amyloidogenic behavior. The X-ray structure of FL AL55 and data from hydrogen-deuterium exchange mass spectrometry unveil an open conformation of the two VLs in the dimeric structure, featuring a highly dynamic interface distinct from closed conformations observed in other known toxic LCs. This open structure enhances the VL’s susceptibility to proteolytic digestion, potentially facilitating amyloid formation from the isolated VL domain. Investigation into isolated domains confirms that the isolated VL is less structured, unstable, and dynamic in the CDR1 and CDR2 regions, correlating with its higher aggregation under _in-vitro_ conditions. Additionally, unfolding and refolding kinetic experiments provide in-depth insight into the slow unfolding rates of FL and CL but the fast unfolding rate of VL which confirms the rate-limiting step in FL unfolding is stable CL domain. However, limited refolding due to the slow refolding rate of the VL domain confirms a shift of folding transition towards a misfolded conformation which might favor aggregation. Cytotoxicity assay in _C. elegans_ shows soluble toxicity of FL AL55. Additionally, highly polymorphic amyloid fibrils formed by VL show that _in-vitro_ formed fibrils are not truly representative of _in-vivo_ deposited fibrils. Collectively, this research yields crucial insights into the structural and biophysical features influencing AL55 amyloidogenic behavior, presenting potential avenues for therapeutic intervention.



Determinants of amyloidogenic behavior in AL amyloidosis patient-derived AL55 light chain: Insights from structural and biophysical studies PA20 (#39)

We invite you to attend the XIX International Symposium on Amyloidosis to be held in Rochester, MN.

This symposium is organized as a hybrid meeting (with the focus on in-person) held from Sunday, May 26 through Thursday, May 30, 2024.

Together with the ISA Board and members of Mayo Clinic, a very attractive scientific hybrid program is being planned. The program will cover a variety of types of systemic amyloidosis: ATTR (hereditary and wild-type), AL (light-chain), AA and less frequent forms. There will be key lectures, specific symposia including those company sponsored, oral presentations and poster sessions of accepted abstracts.

COURSE DESCRIPTION
This program will provide a comprehensive review of state-of-the-art education in systemic amyloidosis: basic science, pathophysiology, diagnosis, current and emerging treatments. Scientific presentations will include competitive oral and poster abstracts. The rapid evolution of scientific discovery and expanding treatment options has created tremendous interest in the field and this meeting will fill and important gap in educating scientists and clinicians.